Lithographic printing plate precursor and lithographic printing process

ABSTRACT

A lithographic printing plate precursor, which comprises: a support; an image-recording layer; and a protective layer, in this order, wherein at least one of the image-recording layer and the protective layer comprises a phosphonium salt having a specific structure, and a lithographic printing process, which comprises: exposing a lithographic printing plate precursor; supplying an oil-based ink and a fountain solution comprising a phosphonium salt having a specific structure to the exposed lithographic printing plate precursor on a printing machine to remove an unexposed area of an image-recording layer; and conducting printing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of pending U.S. application Ser. No.11/505,468, filed on Aug. 17, 2006, which claims the benefit of JapaneseApplication No. P2005-238820, filed on Aug. 19, 2005, both of which arehereby incorporated by reference as fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithographic printing plate precursorand lithographic printing process. More particularly, the inventionrelates to a lithographic printing plate precursor which gives alithographic printing plate stably showing ink receptibility duringprinting and having excellent printing durability, and to lithographicprinting process.

2. Description of the Related Art

A lithographic printing plate generally has oleophilic image areas whichreceive an ink during printing and hydrophilic nonimage areas whichreceive a fountain solution. Lithographic printing is a process in whichthe surface of a lithographic printing plate is made to have adifference in ink adhesion by forming oleophilic image areas asink-receiving areas and hydrophilic nonimage areas asfountain-solution-receiving areas (non-ink-receiving areas) based on thefact that water has the property of repelling oil-based inks, and an inkis adhered only to the image areas and then transferred to a material tobe printed, e.g., paper, to conduct printing.

A lithographic printing plate precursor (PS plate) comprising ahydrophilic support and an oleophilic photosensitive resin layer(image-recording layer) formed thereon has hitherto been in wide use forproducing such lithographic printing plate therefrom. Usually, alithographic printing plate is produced from a lithographic printingplate precursor by a method which comprises exposing the precursorthrough an original, e.g., a lith film, and then dissolving and removingthose unnecessary parts of the image-recording layer which becomenonimage areas with an alkaline developing solution or organic solventto thereby expose the corresponding surface parts of the hydrophilicsupport and form nonimage areas while leaving those parts of theimage-recording layer which become image areas.

Such platemaking processes heretofore in use for producing a printingplate from a lithographic printing plate precursor necessitate a step inwhich unnecessary parts of the image-recording layer after exposure aredissolved and removed with a developing solution or the like. However,to eliminate or simplify such a wet treatment performed additionally isone of the subjects to be accomplished. In particular, the discard ofwaste liquids resulting from wet treatments has recently become a matterof considerable concern of the whole industrial world from thestandpoint of care of the global environment and, hence, there is anincreasingly growing desire for the accomplishment of that subject.For this purpose, a technique called on-press development has beenproposed as a simple platemaking method. In this technique is used animage-recording layer whose unnecessary parts can be removed in anordinary printing process. After exposure, the unnecessary parts of theimage-recording layer are removed on a printing machine to obtain alithographic printing plate.

Examples of the on-press development include: a method which uses alithographic printing plate precursor having an image-recording layercapable of being dissolved or dispersed in a fountain solution or inksolvent or in a fountain solution/ink emulsion; a method in which animage-recording layer is mechanically removed by contact with rollers orthe blanket of a printing machine; and a method in which the cohesiveforce of an image-recording layer or adhesion between theimage-recording layer and the support is reduced by the penetration of afountain solution, ink solvent, or the like and, thereafter, theimage-recording layer is mechanically removed by contact with rollers orthe blanket.

In the invention, the term “development step” means, unless otherwiseindicated, a step in which an apparatus (usually, an automaticprocessor) other than printing machines is used to remove unexposedareas of the image-recording layer of a lithographic printing plateprecursor by contact with a liquid (usually, an alkaline developingsolution) to expose a surface of the hydrophilic support. Furthermore,the term “on-press development” herein means, unless otherwiseindicated, a method and step in which a printing machine is used toremove unexposed areas of the image-recording layer of a lithographicprinting plate precursor by contact with a liquid (usually, a printingink and/or a fountain solution) to expose a surface of the hydrophilicsupport.

However, in the case of using the related-art image-recording layer inwhich images are recorded with ultraviolet or visible light, it has beennecessary to employ a troublesome procedure in which the lithographicprinting plate precursor which has been exposed is, for example, kept ina completely light-shielded state or under constant-temperatureconditions until it is mounted on a printing machine because theimage-recording layer does not fix even after the exposure.On the other hand, digitization technology in which image information iselectronically processed, accumulated, and outputted by a computer hasrecently come to spread extensively, and various new image outputtechniques suitable for such digitization technology have come to bepractically used. Under these circumstances, attention is focused on acomputer-to-plate technique in which a highly convergent radiation suchas a laser light is caused to carry digitized image information and thislight is used to scan and expose a lithographic printing plate precursorto directly produce a lithographic printing plate without via a lithfilm. Consequently, to obtain a lithographic printing plate precursorsuitable for such a technique has become one of important technicalsubjects.

As described above, simplification of platemaking and use of a dryplatemaking process involving no development step have recently come tobe more strongly desired than before from the standpoints of care of theglobal environment and suitability for digitization. High-output laserssuch as a semiconductor laser emitting infrared rays having a wavelengthof from 760 to 1,200 nm and a YAG laser have recently become availableat low cost. Because of this, a process for lithographic printing plateproduction using any of these high-output lasers as a device for imagerecording is coming to be regarded as a promising process which employsscanning exposure and is easy to incorporate into the digitizationtechnology.

In the conventional platemaking process, a photosensitive lithographicprinting plate precursor is imagewise exposed at a low to mediumilluminance to record an image based on an imagewise property changecaused by a photochemical reaction in the image-recording layer. Incontrast, in the above-described process using a high-output laser, alarge quantity of light energy is applied to exposed areas in anextremely short time period to efficiently convert the light energy toheat energy and the image-recording layer is caused by this heat tothermally undergo a change such as a chemical change, phase change, orchange in form or structure. This change is utilized for imagerecording. Consequently, although image information is inputted by meansof light energy such as laser light, image recording is influenced notonly by the light energy but also by the reaction caused by heat energy.Usually, the recording technique utilizing the heat generated by suchhigh-power-density exposure is called heat mode recording, and theconversion of light energy into heat energy is called light/heatconversion.

Great merits of platemaking processes employing heat mode recording arethat the image-recording layer is not sensitive to light on an ordinaryilluminance level, such as indoor light, and that an operation forfixing the image recorded by high-illuminance exposure is not essential.Namely, there is no possibility that the lithographic printing plateprecursor for use in heat mode recording might be influenced by indoorlight before exposure, and it is not essential to conduct an operationfor image fixing after exposure. Consequently, when there is alithographic printing plate precursor capable of on-press developmentwhich employs an image-recording layer which is insolubilized orsolubilized by exposure with, e.g., a high-output laser, then a printingsystem is possible in which the image is not influenced even when theimage-recording layer after the exposure is exposed to indoor ambientlight. Namely, it is expected that when heat mode recording is utilized,a lithographic printing plate precursor suitable for on-pressdevelopment can be obtained. However, most of the related-artphotosensitive recording materials practically useful as image-recordinglayers are sensitive to light in the visible region having wavelengthsof 760 nm and shorter and, hence, image recording therein with aninfrared laser is impossible. Because of this, there is a desire for amaterial capable of image recording with an infrared laser.Under these circumstances, Japanese Patent No. 2938397, for example,describes a lithographic printing plate precursor comprising ahydrophilic support and, formed thereon, an image-forming layercomprising a hydrophilic binder and hydrophobic thermoplastic-polymerparticles dispersed therein. There is a description in Japanese PatentNo. 2938397 to the effect that this lithographic printing plateprecursor can be used in the following manner. The precursor is exposedwith an infrared laser to thermally bond the hydrophobicthermoplastic-resin particles to one another and thereby form an image.Thereafter, this precursor is attached to the cylinder of a printingmachine and developed thereon with a fountain solution and/or an ink.

The technique described above in which an image is formed by the merebonding of fine particles by thermal fusion attains satisfactoryon-press developability. However, this technique has had a problem thatimage strength (adhesion to the support) is considerably low andprinting durability is insufficient.

On the other hand, JP-A-2001-277740 and JP-A-2001-277742 describe alithographic printing plate precursor which comprises a hydrophilicsupport and deposited thereon microcapsules containing a polymerizablecompound.

Furthermore, JP-A-2002-287334 describes a lithographic printing plateprecursor comprising a support and formed thereon a photosensitive layer(image-recording layer) comprising an infrared absorber, a radicalpolymerization initiator, and a polymerizable compound.

Those techniques utilizing a polymerization reaction have a feature inthat image strength is relatively satisfactory because the image areashave a higher chemical-bond density than the image areas formed by thethermal fusion bonding of fine polymer particles. However, the radicalpolymerization type photosensitive layer has a feature in that it is aptto be influenced by oxygen during image formation. It has hence beennecessary to form a protective layer comprising a hydrophilic resinhaving high oxygen barrier properties, such as poly(vinyl alcohol). Sucha protective layer has had drawbacks that the removal thereof inon-press development requires much times to incur a large paper loss andthat in case where the protective layer is not completely removed andremains in a slight amount on the image areas, then the residue attractsa hydrophilic ingredient in the fountain solution to reduce inkreceptibility. The reduced ink receptibility arouses troubles, forexample, that the image areas during printing come to suffer inkadhesion failures, resulting in reduced printing durability. Forovercoming these drawbacks, it is effective to add a hydrophiliccompound to the protective layer and the image-recording layer andthereby enhance the penetration of a fountain solution in on-pressdevelopment. However, this technique has had a problem that the additionof a hydrophilic compound simultaneously reduces the image strength andink receptibility of the image areas and, hence, satisfactory printedmatters are not obtained.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a lithographicprinting plate precursor which gives a lithographic printing platestably showing ink receptibility during printing and having excellentprinting durability. Another object of the invention is to provide alithographic printing plate precursor in which an image can be recordedwith a laser and which, after the image recording, can be satisfactorilydeveloped on a printing machine without via a development step to give aprinting plate stably showing ink receptibility during printing andhaving excellent printing durability. Still another object of theinvention is to provide a lithographic printing process which includesimage recording with a laser and on-press development and which attainsstable ink receptibility during printing and excellent printingdurability while maintaining satisfactory on-press developability.

The present inventor made intensive investigations on the problemsdescribed above. As a result, it was found that a specific phosphoniumcompound is effective in attaining an excellent balance between on-pressdevelopability and the ink receptibility of image areas. The inventionhas been thus achieved.The invention provides the following.

(1) A lithographic printing plate precursor, which comprises:

a support;

an image-recording layer; and

a protective layer, in this order,

wherein at least one of the image-recording layer and the protectivelayer comprises a phosphonium salt represented by formula (1):

wherein Ar₁ to Ar₆ each independently represents an aryl group or aheterocyclic group;

L represents a divalent connecting group;

X represents a counter anion having a valence of n;

n represents an integer of from 1 to 3; and

m is a number satisfying n×m=2.

(2) A lithographic printing plate precursor, which comprises:

a support;

an image-recording layer; and

a protective layer, in this order,

wherein at least one of the image-recording layer and the protectivelayer comprises a phosphonium salt represented by formula (2):

wherein Ar₁ to Ar₆ each independently represents an aryl group havingfrom 6 to 15 carbon atoms;

L represents a divalent connecting group;

R represents an alkyl group, an aryl group, a heterocyclic group, analkoxy group, an alkylamino group or an arylamino group;

n represents an integer of from 1 to 3; and

m is a number satisfying n×m=2.

(3) The lithographic printing plate precursor as described in (1) or (2)above,

wherein the image-recording layer further comprises an infraredabsorber.

(4) The lithographic printing plate precursor as described in any of (1)to (3) above,

wherein the image-recording layer further comprises a radicalpolymerization initiator and a radical-polymerizable compound.

(5) The lithographic printing plate precursor as described in any of (1)to (4) above,

wherein the protective layer further comprises an inorganic layercompound.

(6) The lithographic printing plate precursor as described in any of (1)to (5) above, which can be developed on a printing machine afterimagewise exposure.

(7) A lithographic printing process, which comprises:

imagewise exposing a lithographic printing plate precursor as describedin (6) above;

mounting the printing plate precursor on a printing machine without viaa development step; and

conducting printing, or

mounting a lithographic printing plate precursor as described in (6)above on a printing machine; then

imagewise exposing the printing plate precursor; and

conducting printing.

(8) A lithographic printing process, which comprises:

exposing a lithographic printing plate precursor, so as to form anexposed lithographic printing plate precursor;

supplying an oil-based ink and a fountain solution to the exposedlithographic printing plate precursor on a printing machine to remove anunexposed area of an image-recording layer of the exposed lithographicprinting plate precursor; and

conducting printing,

wherein the fountain solution is a fountain solution comprising aphosphonium salt represented by formula (1) or (2):

wherein Ar₁ to Ar₆ each independently represents an aryl group or aheterocyclic group;

L represents a divalent connecting group;

X represents a counter anion having a valence of n;

n represents an integer of from 1 to 3; and

m is a number satisfying n×m=2:

wherein Ar₁ to Ar₆ each independently represents an aryl group havingfrom 6 to 15 carbon atoms;

L represents a divalent connecting group;

R represents an alkyl group, an aryl group, a heterocyclic group, analkoxy group, an alkylamino group or an arylamino group;

n represents an integer of from 1 to 3; and

m is a number satisfying n×m=2.

(9) A phosphonium salt represented by formula (2):

wherein Ar₁ to Ar₆ each independently represents an aryl group havingfrom 6 to 15 carbon atoms;

L represents a divalent connecting group;

R represents an alkyl group, an aryl group, a heterocyclic group, analkoxy group, an alkylamino group or an arylamino group;

n represents an integer of from 1 to 3; and

m is a number satisfying n×m=2.

On-press developability and ink receptibility could be reconciled in theinvention by incorporating a phosphonium salt represented by formula (1)in a lithographic printing plate precursor or a fountain solution.

Phosphonium compounds have generally been known from long ago asphotosensitive acid generators as apparent from the fact that suchapplication is shown in, e.g., JP-A-50-158698. Furthermore, to add aphosphonium compound to a fountain solution and cause the compound tofunction as a protective agent for the image areas of a PS plate isknown as apparent from the fact that it is disclosed in, e.g.,JP-A-5-112085. However, those patent documents neither disclose norsuggest any technique effective in accomplishing the subject in on-pressdevelopment type plate precursor systems as in the invention thatexposed area of a protective layer comprising a hydrophilic resin as themain component are removed and inhibited from being readsorbed whilemaintaining the penetration of a fountain solution during on-pressdevelopment.

DETAILED DESCRIPTION OF THE INVENTION

The lithographic printing plate precursor of the invention ischaracterized in that a specific phosphonium salt is contained in theimage-recording layer or the protective layer. One of the lithographicprinting processes of the invention is characterized in that a fountainsolution containing the specific phosphonium salt is used.

[Phosphonium Salt]

The phosphonium salt represented by formula (1) to be used in thelithographic printing plate precursor of the invention is describedbelow.

In the formula, Ar₁ to Ar₆ each independently represent an aryl group ora heterocyclic group; L represents a divalent connecting group; Xrepresents a counter anion having a valence of n; n represents aninteger of 1-3; and m is a number satisfying n×m=2. Preferred examplesof the aryl group include phenyl, naphthyl, tolyl, xylyl, fluorophenyl,chlorophenyl, bromophenyl, methoxyphenyl, ethoxyphenyl, dimethoxyphenyl,methoxycarbonylphenyl, and dimethylaminophenyl. Examples of theheterocyclic group include pyridyl, quinolyl, pyrimidinyl, thienyl, andfuryl.

The divalent connecting group represented by L is a connecting groupcomprising one or more nonmetallic atoms. Specifically, it comprises1-60 carbon atoms, 0-10 nitrogen atoms, 0-50 oxygen atoms, 1-100hydrogen atoms, and 0-20 sulfur atoms. More specific examples of theconnecting group include ones each comprising a combination of two ormore of the following structural units.

In the case where the divalent connecting group represented by L has oneor more substituents, examples of the substituents include alkyl groupshaving 1-20 carbon atoms, such as methyl and ethyl, aryl groups having6-16 carbon atoms such as phenyl and naphthyl, hydroxyl, carboxyl,sulfonamide groups, N-sulfonylamide groups, acyloxy groups having 1-6carbon atoms, such as acetoxy, alkoxy groups having 1-6 carbon atoms,such as methoxy and ethoxy, halogen atoms such as chlorine and bromine,alkoxycarbonyl groups having 2-7 carbon atoms, such as methoxycarbonyl,ethoxycarbonyl, and cyclohexyloxycarbonyl, cyano, and carbonic estergroups such as t-butyl carbonate.

Preferred examples of the connecting group L include the following.Especially preferred of these are the connecting groups having 6-12carbon atoms.

Preferred examples of the counter anion X include halogen anions,nitrate anion, sulfate anion, phosphate anion, sulfonate anions,carboxylate anions, PF₆, BF₄, perchlorate anion, and tetraarylborateanions. Especially preferred are phosphonium salts represented by thefollowing formula (2), in which the counter anion is a sulfonate anion.Use of a phosphonium salt represented by formula (2) in the on-pressdevelopment type lithographic printing plate precursor is effective inimproving on-press developability.

In the formula, R represents an alkyl, aryl, heterocyclic, alkoxy,alkylamino, or arylamino group. Ar₁ to Ar₆, L, m, and n have the samemeanings as in formula (1).Specific examples of the counter anion in formula (2) are shown below.

Specific examples of the phosphonium salt represented by formula (1) or(2) to be used in the invention are shown below.

Examples of the synthesis of phosphonium salts for use in the inventionare shown below.

Synthesis of Nonamethylenebis(triphenylphosphonium)Dibromide

28.61 Grams of 1,9-dibromononane and 52.46 g of triphenylphosphine wereweighed out and placed in a 500-mL three-necked flask. These compoundswere dissolved in 100 mL of N-methylpyrrolidone. This solution wasstirred at 80° C. for 5 hours and the resultant reaction mixture wascooled to room temperature. Thereafter, the reaction mixture was pouredinto 500 mL of ethyl acetate kept being sufficiently stirred. The solidprecipitated was collected by suction filtration and washed with 50 mLof ethyl acetate twice. The solid obtained was placed on a Petri dishand dried at room temperature under vacuum until the mass of the solidbecame constant. As a result,nonamethylenebis(triphenylphosphonium)dibromide was obtained as a whitesolid in an amount of 73 g (yield: 90%).

Synthesis of Nonamethylenebis(triphenylphosphonium)Di(dimethyl5-Sulfoisophthalate) (P-8)

29.62 Grams of sodium dimethyl 5-sulfoisophthalate and 118.48 g of waterwere weighed out and placed in a 500-mL three-necked flask. The contentswere heated to 80° C. to completely dissolve the salt. On the otherhand, 16.22 g of nonamethylenebis (triphenylphosphonium)dibromide and16.22 g of water were weighed out and placed in a 100-mL eggplant typeflask, and the contents were heated to 80° C. to completely dissolve thesalt. The aqueous nonamethylenebis(triphenylphosphonium)dibromidesolution thus obtained was added to the aqueous sodium dimethyl5-sulfoisophthalate solution kept being stirred at 80° C. The resultantmixture was continuously stirred for 1 hour under the same conditions.After the 1-hour stirring, heating was stopped and the mixture wasallowed to cool. At the time when the temperature reached 70° C., 34 mLof acetone was added. The resultant mixture was allowed to cool whilecontinuously stirring it under the same conditions.

At the time when the liquid reaction mixture opacified (about 63° C.),seed crystals of the target compound were added thereto. After themixture was allowed to cool to room temperature, it was cooled on an icebath and continuously stirred for 2 hours at an internal temperature ofabout 0° C. After the 2-hour stirring, the solid precipitated wascollected by suction filtration and washed with 400 mL of distilledwater. The solid obtained was placed in a 1-L beaker and 400 mL ofdistilled water was added thereto. This mixture was continuously stirredat room temperature for 1 hour. The solid was collected by suctionfiltration and washed with 100 mL of distilled water twice. The solidobtained was placed on a Petri dish and dried at 50° C. under vacuumuntil the mass of the solid became constant. As a result,nonamethylenebis(triphenylphosphonium)di(dimethyl 5-sulfoisophthalate)(P-8) was obtained as a white solid in an amount of 19.6 g (yield: 82%).

[Image-Recording Layer]

The image-recording layer in the invention preferably contains aninfrared absorber so as to be capable of recording by infraredirradiation. Furthermore, the image-recording layer preferably is onecontaining a radical polymerization initiator and aradical-polymerizable compound. Moreover, the image-recording layer inthe invention preferably is one in which, after exposure, the unexposedareas can be removed on a printing machine by supplying an oil-based inkand an aqueous ingredient thereto without via any development step.

In the lithographic printing plate precursor having such a composition,when the image-recording layer is irradiated with infrared, the exposedareas of the layer cure to form hydrophobic (oleophilic) regions. Uponinitiation of printing, the unexposed areas are rapidly removed from thesupport surface with a fountain solution and an oily ingredient such asan ink or with an emulsion comprising a fountain solution and an oilyingredient.

<Infrared Absorber>

In the case where the lithographic printing plate precursor of theinvention is subjected to image formation with a laser which emitsinfrared rays of 760-1,200 nm as a light source, it is generallyessential to use an infrared absorber. An infrared absorber has thefunction of converting absorbed infrared rays into heat. The radicalpolymerization initiator (radical generator), which will be describedlater, is pyrolyzed by the resultant heat to generate a radical. Theinfrared absorber to be used in the invention is a dye or pigment havingan absorption maximum in the wavelength range of from 760 to 1,200 nm.

As the dye can be used any of commercial dyes and known dyes describedin the literature, e.g., Senryô Binran (edited by The Society ofSynthetic Organic Chemistry, Japan, published in 1970). Examples thereofinclude dyes such as azo dyes, metal complex azo dyes, pyrazolone azodyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes,carbonium dyes, quinoneimine dyes, methine dyes, cyanine dyes,squarylium dyes, pyrylium salts, and metal thiolate complexes.

Preferred examples of such dyes include the cyanine dyes shown in, e.g.,JP-A-58-125246, JP-A-59-84356, and JP-A-60-78787, the methine dyes shownin, e.g., JP-A-58-173696, JP-A-58-181690, and JP-A-58-194595, thenaphthoquinone dyes shown in, e.g., JP-A-58-112793, JP-A-58-224793,JP-A-59-48187, JP-A-59-73996, JP-A-60-52940, and JP-A-60-63744, thesquarylium dyes shown in, e.g., JP-A-58-112792, and the cyanine dyesshown in British Patent No. 434,875.

The near-infrared-absorbing sensitizer described in U.S. Pat. No.5,156,938 also is advantageously used. Furthermore, the substitutedarylbenzo(thio)pyrylium salts shown in U.S. Pat. No. 3,881,924, thetrimethinethiapyrylium salts shown in JP-A-57-142645 (U.S. Pat. No.4,327,169), the pyrylium compounds shown in JP-A-58-181051,JP-A-58-220143, JP-A-59-41363, JP-A-59-84248, JP-A-59-84249,JP-A-59-146063, and JP-A-59-146061, the cyanine dyes shown inJP-A-59-216146, the pentamethinethiopyrylium salts shown in U.S. Pat.No. 4,283,475, and the pyrylium compounds shown in JP-B-5-13514 andJP-B-5-19702 are advantageously used. Other preferred examples of thedye include the near-infrared-absorbing dyes represented by the formulae(1) and (II) shown in U.S. Pat. No. 4,756,993.

Other preferred examples of the infrared-absorbing dye in the inventioninclude the specific indolenine cyanine dyes shown below, which aregiven in JP-A-2002-278057.

Especially preferred of those dyes are cyanine dyes, squarylium dyes,pyrylium salts, nickel thiolate complexes, and indolenine cyanine dyes.More preferred are cyanine dyes and indolenine cyanine dyes. Anespecially preferred example is a cyanine dye represented by thefollowing formula (i).

In formula (i), X¹ represents a hydrogen atom, halogen atom, —NPh₂,X²-L¹, or the group shown below, wherein X² represents an oxygen atom,nitrogen atom, or sulfur atom and L¹ represents a hydrocarbon grouphaving 1-12 carbon atoms, an aromatic ring having one or moreheteroatoms, or a hydrocarbon group having 1-12 carbon atoms andcontaining one or more heteroatoms. The term heteroatoms herein means N,S, O, halogen atoms, and Se. Xa⁻ has the same meaning as Za⁻, which willbe described later. R^(a) represents a hydrogen atom or a substituentselected from alkyl groups, aryl groups, a substituted or unsubstitutedamino group, and halogen atoms.

R¹ and R² each independently represent a hydrocarbon group having 1-12carbon atoms. From the standpoint of the storage stability of a coatingfluid for recording layer formation, R¹ and R² preferably arehydrocarbon groups having 2 or more carbon atoms, and especiallypreferably are bonded to each other to form a 5- or 6-membered ring.Ar¹ and Ar² may be the same or different and each represent an aromatichydrocarbon group which may have one or more substituents. Preferredexamples of the aromatic hydrocarbon group include a benzene ring and anaphthalene ring. Preferred examples of the substituents includehydrocarbon groups having up to 12 carbon atoms, halogen atoms, andalkoxy groups having up to 12 carbon atoms. Y¹ and Y² may be the same ordifferent and each represent a sulfur atom or a dialkylmethylene grouphaving up to 12 carbon atoms. R³ and R⁴ may be the same or different andeach represent a hydrocarbon group having up to 20 carbon atoms andoptionally having one or more substituents. Preferred examples of thesubstituents include alkoxy groups having up to 12 carbon atoms,carboxyl, and sulfo. R⁵, R⁶, R⁷, and R⁸ may be the same or different andeach represent a hydrogen atom or a hydrocarbon group having up to 12carbon atoms. From the standpoint of starting-material availability, R⁵,R⁶, R⁷, and R⁸ preferably are hydrogen atoms. Za⁻ represents a counteranion, provided that when the cyanine dye represented by formula (1) hasan anionic substituent in its structure and does not necessitate chargeneutralization, then Za⁻ is not necessary. From the standpoint of thestorage stability of a coating fluid for recording layer formation,preferred examples of Za⁻ are a halogen ion, perchlorate ion,tetrafluoroborate ion, hexafluorophosphate ion, and sulfonate ion.Especially preferred are a perchlorate ion, hexafluorophosphate ion, andarylsulfonate ion.Examples of the cyanine dye represented by formula (1) which aresuitable for use in the invention include the cyanine dyes shown inJP-A-2001-133969, paragraphs [0017] to [0019].

Other especially preferred examples thereof include the specificindolenine cyanine dyes given in JP-A-2002-278057 which were shownabove.

As the pigment for use in the invention can be utilized any ofcommercial pigments and pigments described in Color Index (C.I.) Binran,Saishin Ganryô Binran (edited by Japan Association of PigmentTechnology, published in 1977), Saishin Ganryô Ôyô Gijutsu (CMCPublishing Co., Ltd. published in 1986), and Insatsu Inki Gijutsu (CMCPublishing Co., Ltd. published in 1984).

Examples of the kinds of such pigments include black pigments, yellowpigments, orange pigments, brown pigments, red pigments, violetpigments, blue pigments, green pigments, fluorescent pigments, metalpowder pigments, and polymer-bonded dyes. Specific examples thereofinclude insoluble azo pigments, azo lake pigments, condensation azopigments, chelate azo pigments, phthalocyanine pigments, anthraquinonepigments, perylene and perinone pigments, thioindigo pigments,quinacridone pigments, dioxazine pigments, isoindolinone pigments,quinophthalone pigments, dyed lake pigments, azine pigments, nitrosopigments, nitro pigments, natural pigments, fluorescent pigments,inorganic pigments, and carbon black. Preferred of these pigments iscarbon black. Those pigments may be used without being surface-treated,or may be used after having undergone a surface treatment.

Possible techniques for the surface treatment include a method in whichthe pigment surface is coated with a resin or wax, a method in which asurfactant is adhered, and a method in which a reactive substance (e.g.,a silane coupling agent, epoxy compound, or polyisocyanate) is bonded tothe pigment surface. These surface treatment techniques are described inKinzoku Sekken No Seishitsu To Ôyô (Saiwai Shobo), Insatsu Inki Gijutsu(CMC Publishing Co., Ltd., published in 1984), and Saishin Ganryô ÔyôGijutsu (CMC Publishing Co., Ltd., published in 1986).

The particle diameter of the pigment is in the range of preferably0.01-10 μm, more preferably 0.05-1 μm, especially preferably 0.1-1 μm.When the pigment has a particle diameter within this range, a pigmentdispersion which is satisfactorily stable in a coating fluid forimage-recording layer formation and an image-recording layer havingsatisfactory evenness are obtained.For dispersing the pigment, known dispersion techniques for use in inkproduction, toner production, or the like can be used. Examples ofdispersing machines include an ultrasonic disperser, sand mill,attritor, pearl mill, supermill, ball mill, impeller, disperser, KDmill, colloid mill, dynatron, three-roll mill, and pressure kneader.Such dispersion techniques are described in detail in Saishin Ganryô ÔyôGijutsu (CMC Publishing Co., Ltd., published in 1986).Those infrared absorbers may be added to the same layer as otheringredients or may be added to another layer separately formed. However,the infrared absorbers are added so that the image-recording layer ofthe negative lithographic printing plate precursor produced has anabsorbance in the range of 0.3-1.2 when examined by the reflectionmethod at an absorption-maximum wavelength in the wavelength range of760-1,200 nm. Preferably, the absorbance thereof is in the range of0.4-1.1. When the image-recording layer has an absorbance within thatrange, polymerization reaction proceeds evenly throughout the wholedepth of the image-recording layer to give image areas satisfactory infilm strength and adhesion to the support.The absorbance of the image-recording layer can be regulated by changingthe amount of the infrared absorber to be added to the image-recordinglayer and the thickness of the image-recording layer. For measuring theabsorbance, ordinary methods can be used. Examples of usable methodsinclude a method in which an image-recording layer is formed on areflective support, e.g., aluminum, in a suitably determined drythickness in the range necessary for the lithographic printing plateprecursor and the reflection density of the layer is measured with anoptical densitometer or is measured with a spectrophotometer by thereflection method using an integrating sphere.

<Radical Polymerization Initiator>

The radical polymerization initiator (hereinafter often referred tosimply as “polymerization initiator”) to be used in the invention is acompound which generates a radical by the action of light energy or heatenergy or both and thereby initiate and accelerate the polymerization ofcompounds having a polymerizable unsaturated group. Examples ofpolymerization initiators usable in the invention include known heatpolymerization initiators, compounds having a low bond dissociationenergy, and photopolymerization initiators. Of these, preferredpolymerization initiators for use in the invention are compounds whichgenerate a radical by the action of heat energy and thereby initiate andaccelerate the polymerization of compounds having a polymerizableunsaturated group.

Such polymerization initiators for use in the invention will beexplained below in more detail. These polymerization initiators may beused alone or in combination of two or more thereof.

Examples of those polymerization initiators include organic halogencompounds, carbonyl compounds, organic peroxides, azo polymerizationinitiators, azide compounds, metallocene compounds, hexaarylbiimidazolecompounds, organoboron compounds, disulfone compounds, oxime estercompounds, and onium salt compounds.Examples of the organic halogen compounds include the compounds given inWakabayashi et al., Bull. Chem. Soc. Japan, 42, 2924 (1969), U.S. Pat.No. 3,905,815, JP-B-46-4605, JP-A-48-36281, JP-A-53-133428,JP-A-55-32070, JP-A-60-239736, JP-A-61-169835, JP-A-61-169837,JP-A-62-58241, JP-A-62-212401, JP-A-63-70243, JP-A-63-298339, and M. P.Hutt, Journal of Heterocyclic Chemistry, 1 (No. 3), (1970). Preferred ofthese are the oxazole compounds and s-triazine compounds substituted byone or more trihalomethyl groups.More preferred are s-triazine derivatives in which at least one mono-,di-, or trihalogenated methyl group is bonded to the s-triazine ring.Specific examples thereof include2,4,6-tris(monochloromethyl)-s-triazine,2,4,6-tris(dichloromethyl)-s-triazine,2,4,6-tris(trichloromethyl)-s-triazine,2-methyl-4,6-bis(trichloromethyl)-s-triazine,2-n-propyl-4,6-bis(trichloromethyl)-s-triazine,2-(α,α,β-trichloroethyl)-4,6-bis(trichloromethyl)-s-triazine,2-phenyl-4,6-bis(trichloromethyl)-s-triazine,2-(p-methoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine,2-(3,4-epoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine,2-(p-chlorophenyl)-4,6-bis(trichloromethyl)-s-triazine,2-[1-(p-methoxyphenyl)-2,4-butadienyl]-4,6-bis(trichloromethyl)-s-triazine, 2-styryl-4,6-bis(trichloro methyl)-s-triazine,2-(p-methoxystyryl)-4,6-bis(trichloromethyl)-s-triazine,2-(p-isopropyloxystyryl)-4,6-bis(trichloromethyl)-s-triazine,2-(p-tolyl)-4,6-bis(trichloromethyl)-s-triazine,2-(4-methoxynaphthyl)-4,6-bis(trichloromethyl)-s-triazine,2-phenylthio-4,6-bis(trichloromethyl)-s-triazine,2-benzylthio-4,6-bis(trichloromethyl)-s-triazine,2,4,6-tris(dibromomethyl)-s-triazine,2,4,6-tris(tribromomethyl)-s-triazine,2-methyl-4,6-bis(tribromomethyl)-s-triazine, and2-methoxy-4,6-bis(tribromomethyl)-s-triazine.Examples of the carbonyl compounds include benzophenone and derivativesthereof such as Michler's ketone, 2-methylbenzophenone,3-methylbenzophenone, 4-methylbenzophenone, 2-chlorobenzophenone,4-bromobenzophenone, and 2-carboxybenzophenone, acetophenone derivativessuch as 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone,1-hydroxycyclohexyl phenyl ketone, α-hydroxy-2-methylphenylpropanone,1-hydroxy-1-methylethyl p-isopropylphenyl ketone,1-hydroxy-1-(p-dodecylphenyl)ketone,2-methyl-(4′-(methylthio)phenyl)-2-morpholino-1-propanone, and1,1,1-trichloromethyl p-butylphenyl ketone, thioxanthone and derivativesthereof such as 2-ethylthioxanthone, 2-isopropylthioxanthone,2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone,and 2,4-diisopropylthioxanthone, and benzoic ester derivatives such asethyl p-dimethylaminobenzoate and ethyl p-diethylaminobenzoate.Examples of the azo compounds include the azo compounds given inJP-A-8-108621.Examples of the organic peroxides include trimethylcyclohexanoneperoxide, acetylacetone peroxide,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(tert-butylperoxy)cyclohexane, 2,2-bis(tert-butylperoxy)butane,tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzenehydroperoxide, 2,5-dimethylhexane 2,5-dihydroperoxide,1,1,3,3-tetramethylbutyl hydroperoxide, tert-butyl cumyl peroxide,dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane,2,5-oxanoyl peroxide, succinic acid peroxide, benzoyl peroxide,2,4-dichlorobenzoyl peroxide, diisopropyl peroxydicarbonate,di-2-ethylhexyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate,dimethoxyisopropyl peroxycarbonate,di(3-methyl-3-methoxybutyl)peroxydicarbonate, tert-butyl peroxyacetate,tert-butyl peroxypivalate, tert-butyl peroxylaurate, tosyl carbonate,3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(t-hexylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(p-isopropylcumylperpoxycarbonyl)benzophenone,carbonyldi(t-butyl peroxydihydrodiphthalate), and carbonyldi(t-hexylperoxydihydrodiphthalate).Examples of the metallocene compounds include the various titanocenecompounds given in JP-A-59-152396, JP-A-61-151197, JP-A-63-41484,JP-A-2-249, JP-A-2-4705, and JP-A-5-83588, such as, e.g.,di-cyclopentadienyl-Ti-bisphenyl,di-cyclopentadienyl-Ti-bis-2,6-difluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,4,6-trifluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl,di-methylcyclopentadienyl-Ti-bis-2,6-diflorophen-1-yl,di-methylcyclopentadienyl-Ti-bis-2,4,6-trifluorophen-1-yl,di-methylcyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl, anddi-methylcyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl, and theiron-arene complexes given in JP-A-1-304453 and JP-A-1-152109.Examples of the hexaarylbiimidazole compounds include the variouscompounds given in JP-B-6-29285 and U.S. Pat. Nos. 3,479,185, 4,311,783,and 4,622,286. Specific examples thereof include2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o-bromophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o,p-dichlorophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetra(m-methoxyphenyl)biimidazole,2,2′-bis(o,o′-dichlorophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o-nitrophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o-methylphenyl)-4,4′,5,5′-tetraphenylbiimidazole, and2,2′-bis(o-trifluorophenyl)-4,4′,5,5′-tetraphenylbiimidazole.

Examples of the organoboron compounds include the organic boric acidsalts given in JP-A-62-143044, JP-A-62-150242, JP-A-9-188685,JP-A-9-188686, JP-A-9-188710, JP-A-2000-131837, JP-A-2002-107916,Japanese Patent No. 2764769, JP-A-2002-116539, and Kunz, Martin, RadTech '98. Proceeding, Apr. 19-22, 1998, Chicago, the organicboron-sulfonium complexes or organic boron-oxosulfonium complexes givenin JP-A-6-157623, JP-A-6-175564, and JP-A-6-175561, the organicboron-iodonium complexes given in JP-A-6-175554 and JP-A-6-175553, theorganic boron-phosphonium complexes given in JP-A-9-188710, and theorganic boron-transition metal coordination complexes given inJP-A-6-348011, JP-A-7-128785, JP-A-7-140589, JP-A-7-306527, andJP-A-7-292014.

Examples of the disulfone compounds include the compounds given inJP-A-61-166544 and JP-A-2003-328465.Examples of the oxime ester compounds include the compounds given in J.C. S. Perkin II (1979) 1653-1660, J. C. S. Perkin II (1979) 156-162,Journal of Photopolymer Science and Technology (1995) 202-232, andJP-A-2000-66385 and the compounds given in JP-A-2000-80068. Specificexamples thereof include the compounds represented by the followingstructural formulae.

Examples of the onium salt compounds include the diazonium salts givenin S. I. Schlesinger, Photogr. Sci. Eng., 18, 387 (1974) and T. S. Balet al., Polymer, 21, 423 (1980), the ammonium salts given in U.S. Pat.No. 4,069,055 and JP-A-4-365049, the phosphonium salts given in U.S.Pat. Nos. 4,069,055 and 4,069,056, the iodonium salts given in EuropeanPatent No. 104,143, U.S. Pat. Nos. 339,049 and 410,201, JP-A-2-150848,and JP-A-2-296514, the sulfonium salts given in European Patents Nos.370,693, 390,214, 233,567, 297,443, and 297,442, U.S. Pat. Nos.4,933,377, 161,811, 410,201, 339,049, 4,760,013, 4,734,444, and2,833,827, German Patents Nos. 2,904,626, 3,604,580, and 3,604,581, theselenonium salts given in J. V. Crivello et al., Macromolecules, 10(6),1307 (1977) and J. V. Crivello et al., J. Polymer Sci., Polymer Chem.Ed., 17, 1047 (1979), and the arsonium salts given in C. S. Wen et al.,Teh. Proc. Conf. Rad. Curing ASIA, p. 478, Tokyo, October (1988).Especially from the standpoints of reactivity and stability, preferredexamples include the oxime ester compounds or onium salts (diazoniumsalts, iodonium salts, or sulfonium salts) shown above. In theinvention, these onium salts function not as acid generators but asionic radical polymerization initiators.The onium salts suitable for use in the invention are onium saltsrepresented by the following formulae (RI-I) to (RI-III).

In formula (RI-I), Ar₁₁ represents an aryl group which has up to 20carbon atoms and may have 1-6 substituents. Preferred examples of thesubstituents include alkyl groups having 1-12 carbon atoms, alkenylgroups having 1-12 carbon atoms, alkynyl groups having 1-12 carbonatoms, aryl groups having 1-12 carbon atoms, alkoxy groups having 1-12carbon atoms, aryloxy groups having 1-12 carbon atoms, halogen atoms,alkylamino groups having 1-12 carbon atoms, dialkylamino groups having1-12 carbon atoms, alkylamide or arylamide groups having 1-12 carbonatoms, carbonyl, carboxyl, cyano, sulfonyl, thioalkyl groups having 1-12carbon atoms, and thioaryl groups having 1-12 carbon atoms. Z₁₁ ⁻represents a monovalent anion. Examples thereof include halogen ions,perchlorate ion, hexafluorophosphate ion, tetrafluoroborate ion,sulfonate ions, sulfinate ions, thiosulfinate ions, and sulfate ion.Preferred of these from the standpoint of safety are perchlorate ion,hexafluorophosphate ion, tetrafluoroborate ion, sulfonate ions, andsulfinate ions.In formula (RI-II), Ar₂₁ and Ar₂₂ each independently represent an arylgroup which has up to 20 carbon atoms and may have 1-6 substituents.Preferred examples of the substituents include alkyl groups having 1-12carbon atoms, alkenyl groups having 1-12 carbon atoms, alkynyl groupshaving 1-12 carbon atoms, aryl groups having 1-12 carbon atoms, alkoxygroups having 1-12 carbon atoms, aryloxy groups having 1-12 carbonatoms, halogen atoms, alkylamino groups having 1-12 carbon atoms,dialkylamino groups having 1-12 carbon atoms, alkylamide or arylamidegroups having 1-12 carbon atoms, carbonyl, carboxyl, cyano, sulfonyl,thioalkyl groups having 1-12 carbon atoms, and thioaryl groups having1-12 carbon atoms. Z₂₁ ⁻ represents a monovalent anion. Examples thereofinclude halogen ions, perchlorate ion, hexafluorophosphate ion,tetrafluoroborate ion, sulfonate ions, sulfinate ions, thiosulfinateions, and sulfate ion. Preferred of these from the standpoints of safetyand reactivity are perchlorate ion, hexafluorophosphate ion,tetrafluoroborate ion, sulfonate ions, sulfinate ions, and carboxylateions.

In formula (RI-III), R₃₁, R₃₂, and R₃₃ each independently represent anaryl, alkyl, alkenyl, or alkynyl group which has up to 20 carbon atomsand may have 1-6 substituents. Aryl groups are preferred of these fromthe standpoints of reactivity and safety. Examples of the substituentsinclude alkyl groups having 1-12 carbon atoms, alkenyl groups having1-12 carbon atoms, alkynyl groups having 1-12 carbon atoms, aryl groupshaving 1-12 carbon atoms, alkoxy groups having 1-12 carbon atoms,aryloxy groups having 1-12 carbon atoms, halogen atoms, alkylaminogroups having 1-12 carbon atoms, dialkylamino groups having 1-12 carbonatoms, alkylamide or arylamide groups having 1-12 carbon atoms,carbonyl, carboxyl, cyano, sulfonyl, thioalkyl groups having 1-12 carbonatoms, and thioaryl groups having 1-12 carbon atoms. Z₃₁ ⁻ represents amonovalent anion. Examples thereof include halogen ions, perchlorateion, hexafluorophosphate ion, tetrafluoroborate ion, sulfonate ions,sulfinate ions, thiosulfinate ions, sulfate ion, and carboxylate ions.Preferred of these from the standpoints of safety and reactivity areperchlorate ion, hexafluorophosphate ion, tetrafluoroborate ion,sulfonate ions, sulfinate ions, and carboxylate ions. More preferredexamples thereof include the carboxylate ions shown in JP-A-2001-343742.Especially preferred examples include the carboxylate ions shown inJP-A-2002-148790.

Specific examples of the onium salt compounds suitable for use in theinvention are shown below, but the onium salt compounds should not beconstrued as being limited to the following examples.

Those polymerization initiators can be added in an amount of 0.1-50% bymass, preferably 0.5-30% by mass, especially preferably 1-20% by mass,based on all solid ingredients constituting the image-recording layer.(In this specification, mass ratio is equal to weight ratio.) When theinitiator amount is within this range, satisfactory sensitivity isobtained and the nonimage areas have satisfactory unsusceptibility toscumming during printing. Those polymerization initiators may be usedalone or in combination of two or more thereof. Any of thosepolymerization initiators and other ingredients may be added to the samelayer. Alternatively, a layer containing any of the polymerizationinitiators may be separately formed.

<Radical-Polymerizable Compound>

The radical-polymerizable compound (hereinafter often referred to simplyas “polymerizable compound”) usable in the invention is anaddition-polymerizable compound having at least one ethylenicallyunsaturated double bond. It is selected from compounds having at leastone, preferably two or more ethylenically unsaturated bonds. Suchcompounds are well known in this industrial field, and can be used inthe invention without particular limitations.

These are in chemical forms such as, e.g., a monomer, a prepolymer,i.e., dimer, trimer, or oligomer, and a mixture of two or more of these.Examples of such polymerizable compounds include unsaturated carboxylicacids (e.g., acrylic acid, methacrylic acid, itaconic acid, crotonicacid, isocrotonic acid, and maleic acid) and esters and amides of these.Preferably, an ester of an unsaturated carboxylic acid with an aliphaticpolyhydric alcohol compound or an amide of an unsaturated carboxylicacid with an aliphatic polyamine compound is used. Also preferably usedare: a product of the addition reaction of an unsaturated carboxylicacid ester or amide having a nucleophilic substituent, such as hydroxyl,amino, or mercapto, with a mono- or polyfunctional isocyanate or epoxy;a product of the dehydrating condensation reaction of the unsaturatedcarboxylic acid ester or amide with a mono- or polyfunctional carboxylicacid; and the like. Furthermore, a product of the addition reaction ofan unsaturated carboxylic acid ester or amide having an electrophilicsubstituent, such as an isocyanate group or epoxy group, with a mono- orpolyfunctional alcohol, amine, or thiol and a product of thesubstitution reaction of an unsaturated carboxylic acid ester or amidehaving an eliminable substituent, such as a halogen group or tosyloxy,with a mono- or polyfunctional alcohol, amine, or thiol are alsopreferred. Other usable examples include compounds obtained throughthese reactions using an unsaturated phosphonic acid, styrene, vinylether, or the like in place of the unsaturated carboxylic acid.

Examples of the monomeric ester of an aliphatic polyhydric alcoholcompound with an unsaturated carboxylic acid include acrylic esters suchas ethylene glycol diacrylate, triethylene glycol diacrylate,1,3-butanediol diacrylate, tetramethylene glycol diacrylate, propyleneglycol diacrylate, neopentyl glycol diacrylate, trimethylolpropanetriacrylate, trimethylolpropane tri(acryloyloxypropyl)ether,trimethylolethane triacrylate, hexanediol diacrylate,1,4-cyclohexanediol diacrylate, tetraethylene glycol diacrylate,pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritoltetraacrylate, dipentaerythritol diacrylate, dipentaerythritolhexaacrylate, sorbitol triacrylate, sorbitol tetraacrylate, sorbitolpentaacrylate, sorbitol hexaacrylate, tri(acryloyloxyethyl)isocyanurate,polyester acrylate oligomers, and isocyanuric acid EO-modifiedtriacrylate.

Examples of methacrylic esters include tetramethylene glycoldimethacrylate, triethylene glycol dimethacrylate, neopentyl glycoldimethacrylate, trimethylolpropane trimethacrylate, trimethylolethanetrimethacrylate, ethylene glycol dimethacrylate, 1,3-butanedioldimethacrylate, hexanediol dimethacrylate, pentaerythritoldimethacrylate, pentaerythritol trimethacrylate, pentaerythritoltetramethacrylate, dipentaerythritol dimethacrylate, dipentaerythritolhexamethacrylate, sorbitol trimethacrylate, sorbitol tetramethacrylate,bis[p-(3-methacryloxy-2-hydroxypropoxy)phenyl]dimethylmethane, andbis[p-(methacryloxyethoxy)phenyl]dimethylmethane.

Examples of itaconic esters include ethylene glycol diitaconate,propylene glycol diitaconate, 1,3-butanediol diitaconate, 1,4-butanedioldiitaconate, tetramethylene glycol diitaconate, pentaerythritoldiitaconate, and sorbitol tetraitaconate. Examples of crotonic estersinclude ethylene glycol dicrotonate, tetramethylene glycol dicrotonate,pentaerythritol dicrotonate, and sorbitol tetradicrotonate. Examples ofisocrotonic esters include ethylene glycol diisocrotonate,pentaerythritol diisocrotonate, and sorbitol tetraisocrotonate. Examplesof maleic esters include ethylene glycol dimaleate, triethylene glycoldimaleate, pentaerythritol dimaleate, and sorbitol tetramaleate.

Examples of other preferred esters include the aliphatic alcohol estersdescribed in JP-B-51-47334 and JP-A-57-196231, the esters having anaromatic framework which are described in JP-A-59-5240, JP-A-59-5241,and JP-A-2-226149, and the esters having an amino group which aredescribed in JP-A-1-165613. The ester monomers mentioned above can beused also as a mixture of two or more thereof.

Examples of the monomeric amide of an aliphatic polyamine compound withan unsaturated carboxylic acid include methylenebisacrylamide,methylenebismethacrylamide, 1,6-hexamethylenebis acrylamide,1,6-hexamethylenebismethacrylamide, diethylenetriaminetrisacrylamide,xylylenebisacrylamide, and xylylenebismethacrylamide. Other preferredexamples of the amide monomer include the amides having a cyclohexylenestructure which are described in JP-B-54-21726.

An addition-polymerizable urethane compound produced by the additionreaction of an isocyanate with hydroxyl groups is also preferred.Examples of this compound include the vinyl urethane compounds havingtwo or more polymerizable vinyl groups per molecule which are describedin JP-B-48-41708. These vinyl urethane compounds are obtained by causinga hydroxyl-containing vinyl monomer represented by the following formula(a) to add to a polyisocyanate compound having two or more isocyanategroups per molecule.

CH₂═C(R₄)COOCH₂CH(R₅)OH  (a)

(In formula (a), R₄ and R₅ each represent H or CH₃.)

Furthermore, the urethane acrylates described in JP-A-51-37193,JP-B-2-32293, and JP-B-2-16765 and the urethane compounds having anethylene oxide-based backbone which are described in JP-B-58-49860,JP-B-56-17654, JP-B-62-39417, and JP-B-62-39418 are also preferred. Inaddition, when any of the addition-polymerizable compounds having anamino structure or sulfide structure in the molecule which are describedin JP-A-63-277653, JP-A-63-260909, and JP-A-1-105238 is used, aphotopolymerizable composition having exceedingly high photosensitivitycan be obtained.

Other examples of the polymerizable compound include polyfunctionalacrylates or methacrylates, such as the polyester acrylates described inJP-A-48-64183, JP-B-49-43191, and JP-B-52-30490 and epoxy acrylatesobtained by reacting an epoxy resin with (meth)acrylic acid. Examplesthereof further include the specific unsaturated compounds described inJP-B-46-43946, JP-B-1-40337, and JP-B-1-40336 and the vinylphosphonicacid compound described in JP-A-2-25493. In some cases, theperfluoroalkyl-containing structure described in JP-A-61-22048 isadvantageously used. Furthermore, the photocurable monomers andoligomers shown in Nihon Setchaku Kyôkai-shi, Vol. 20, No. 7, pp.300-308 (1984) can be used.

Details of the structures of those polymerizable compounds and ofmethods of using these, e.g., as to whether the compounds are used aloneor in combination and the amount of the compounds to be added, can bedetermined at will according to the performance design of the finallithographic printing plate precursor. For example, selections are madefrom the following standpoints.

From the standpoint of sensitivity, a structure having a larger amountof unsaturated bonds per molecule is preferred. In many cases, astructure having a functionality of 2 or higher is preferred. From thestandpoint of enhancing the strength of image areas, i.e., cured film, astructure having a functionality of 3 or higher is preferred. To use acombination of compounds having different functionalities or differentpolymerizable groups (e.g., an acrylic ester, methacrylic ester, styrenecompound, and vinyl ester compound) is an effective method forregulating both sensitivity and strength.

Furthermore, a selection of addition-polymerizable compounds and methodsof using these are important factors which influence compatibility withand dispersibility in other ingredients in the image-recording layer(e.g., the binder polymer, initiator, colorant, etc.). For example,there are cases where use of a low-impurity compound or use of acombination of two or more compounds can improve compatibility. Therealso are cases where a specific structure is selected for the purpose ofimproving adhesion to the substrate or to the protective layer whichwill be described later, etc.

Those polymerizable compounds are used in an amount in the range ofpreferably 5-48% by mass, more preferably 10-45% by mass, based on allsolid ingredients constituting the image-recording layer. Thosecompounds may be used alone or in combination of two or more thereof.

In addition, with respect to methods of using the polymerizablecompounds, it is possible to freely select appropriate structures,proportions, and addition amounts from the standpoints of the degree ofpolymerization inhibition by oxygen, resolution, susceptibility tofogging, refractive index change, surface tackiness, etc. In some cases,a layer constitution/coating method including undercoating andovercoating is possible.

<Binder Polymer>

A binder polymer can be used in the image-recording layer in theinvention in order to improve the film strength of the layer. Any ofknown binder polymers can be used without limitations. Polymers havingfilm-forming properties are preferred. Examples of such binder polymersinclude acrylic resins, poly(vinyl acetal) resins, polyurethane resins,polyurea resins, polyimide resins, polyamide resins, epoxy resins,methacrylic resins, polystyrene resins, novolac type phenolic resins,polyester resins, synthetic rubbers, and natural rubber.

The binder polymer may have crosslinkability so as to improve the filmstrength of image areas. A binder polymer having crosslinkability can beobtained by incorporating crosslinkable functional groups such as, e.g.,ethylenically unsaturated bonds into the main chain or side chains of apolymer. The crosslinkable functional groups may be incorporated bycopolymerization.

Examples of polymers having ethylenically unsaturated bonds in the mainchain of the molecule include poly(1,4-butandiene) andpoly(1,4-isoprene).

Examples of polymers having ethylenically unsaturated bonds in sidechains of the molecule include polymers of esters or amides of acrylicor methacrylic acid, in which the ester or amide residues (i.e., R ineither —COOR or —CONHR) have an ethylenically unsaturated bond.

Examples of the residues (the R) having an ethylenically unsaturatedbond include —(CH₂)_(n)CR¹═CR²R³, —(CH₂O)_(n)CH₂CR¹═CR²R³,—(CH₂CH₂O)_(n)CH₂CR¹═CR²R³, —(CH₂)_(n)NH—CO—O—CH₂CR¹═CR²R³,—(CH₂)_(n)—O—CO—CR¹═CR²R³, and —(CH₂CH₂O)₂—X (wherein R¹ to R³ eachrepresent a hydrogen atom, a halogen atom, or an alkyl, aryl, alkoxy, oraryloxy group having 1 to 20 carbon atoms, provided that R¹ may bebonded to R² or R³ to form a ring; n represents an integer of 1 to 10;and X represents a dicyclopentadienyl residue).

Examples of the ester residues include —CH₂CH═CH₂ (given inJP-B-7-21633), —CH₂CH₂O—CH₂CH═CH₂, —CH₂C(CH₃)═CH₂, —CH₂CH═CH—C₆H₅,—CH₂CH₂OCOCH═CH—C₆H₅, —CH₂CH₂—NHCOO—CH₂CH═CH₂, and —CH₂CH₂O—X (wherein Xrepresents a dicyclopentadienyl residue).

Examples of the amide residues include —CH₂CH═CH₂, —CH₂CH₂—Y (wherein Yrepresents a cyclohexene residue), and —CH₂CH₂—OCO—CH═CH₂.

A binder polymer having crosslinkability cures, for example, by thefollowing mechanism. Free radicals (polymerization initiator radicals orgrowth radicals which are radicals of a polymerizable compound which ispolymerizing) add to crosslinkable functional groups of the binderpolymer to cause addition polymerization directly between polymermolecules or through polymeric chains of the polymerizable compound. Asa result, crosslinks are formed between polymer molecules, whereby thebinder polymer cures. Alternatively, atoms in the polymer (e.g.,hydrogen atoms bonded to the carbon atoms adjacent to the functionalcrosslinkable groups) are withdrawn by free radicals to yield polymerradicals, and these polymer radicals bond to one another to formcrosslinks between polymer molecules, whereby the binder polymer cures.

The content of crosslinkable groups in the binder polymer (content ofradical-polymerizable unsaturated double bonds as determined byiodometric titration) is preferably 0.1-10.0 mmol, more preferably1.0-7.0 mmol, most preferably 2.0-5.5 mmol, per g of the binder polymer.When the content of crosslinkable groups is within this range,satisfactory sensitivity and satisfactory storage stability areobtained.

From the standpoint of improving the removability of unexposed areas ofthe image-recording layer in on-press development, the binder polymerpreferably has high solubility or dispersibility in inks and/or fountainsolutions.

In order for a binder polymer to have improved solubility ordispersibility in inks, it desirably is oleophilic. In order for abinder polymer to have improved solubility or dispersibility in fountainsolutions, it desirably is hydrophilic. Because of this, it is alsoeffective in the invention to use an oleophilic binder polymer and ahydrophilic binder polymer in combination.

Preferred examples of the hydrophilic binder polymer include binderpolymers having hydrophilic groups such as hydroxy, carboxyl,carboxylate, hydroxyethyl, polyoxyethyl, hydroxypropyl, polyoxypropyl,amino, aminoethyl, aminopropyl, ammonium, amide, carboxymethyl, sulfo,or phosphate groups.

Specific examples thereof include gum arabic, casein, gelatin, starchderivatives, carboxymethyl cellulose and the sodium salt thereof,cellulose acetate, sodium alginate, vinyl acetate/maleic acidcopolymers, styrene/maleic acid copolymers, poly(acrylic acid)s andsalts thereof, poly(methacrylic acid)s and salts thereof, homopolymerand copolymers of hydroxyethyl methacrylate, homopolymer and copolymersof hydroxyethyl acrylate, homopolymer and copolymers of hydroxypropylmethacrylate, homopolymer and copolymers of hydroxypropyl acrylate,homopolymer and copolymers of hydroxybutyl methacrylate, homopolymer andcopolymers of hydroxybutyl acrylate, polyethylene glycols,hydroxypropylene polymers, poly(vinyl alcohol)s, hydrolyzed poly(vinylacetate) having a degree of hydrolysis of 60% by mole or higher,preferably 80% by mole or higher, poly(vinyl formal), poly(vinylbutyral), polyvinylpyrrolidone, homopolymer and copolymers ofacrylamide, homopolymer and copolymers of methacrylamide, homopolymerand copolymers of N-methylolacrylamide, alcohol-soluble nylons, andpolyethers of 2,2-bis(4-hydroxyphenyl)propane with epichlorohydrin.

The binder polymer has a mass-average molecular weight of preferably5,000 or higher, more preferably 10,000-300,000, and a number-averagemolecular weight of preferably 1,000 or higher, more preferably2,000-250,000. The polydispersity coefficient (mass-average molecularweight/number-average molecular weight) thereof is preferably 1.1-10.

The binder polymer can be synthesized by known methods. Examples ofsolvents usable for the synthesis include tetrahydrofuran, ethylenedichloride, cyclohexanone, methyl ethyl ketone, acetone, methanol,ethanol, ethylene glycol monomethyl ether, ethylene glycol monoethylether, 2-methoxyethyl acetate, diethylene glycol dimethyl ether,1-methoxy-2-propanol, 1-methoxy-2-propyl acetate, N,N-dimethylformamide,N,N-dimethylacetamide, toluene, ethyl acetate, methyl lactate, ethyllactate, dimethyl sulfoxide, and water. These may be used alone or as amixture of two or more thereof.

A radical polymerization initiator may be used in synthesizing thebinder polymer. As the initiator can be used any of known compounds suchas azo initiators and peroxide initiators.

The content of the binder polymer may be 5-90% by mass and is preferably5-80% by mass, more preferably 10-70% by mass, based on all solidcomponents of the image-recording layer. When the binder polymer contentis within this range, satisfactory image area strength and image-formingproperties are obtained.

It is preferred that the polymerizable compound and the binder polymerbe used in a proportion of from 0.5/1 to 4/1 in terms of mass ratio.

<Microcapsules>

For incorporating those ingredients for image-recording layerconstitution and the other constituent ingredients which will bedescribed later into an image-recording layer in the invention, severalmethods can be used. There are hence several embodiments of theimage-recording layer. One embodiment of the image-recording layer is amolecule dispersion type image-recording layer formed by dissolving theconstituent ingredients in an appropriate solvent and applying thesolution, as described in, e.g., JP-A-2002-287334. Another embodiment isa microcapsule type image-recording layer which contains all or part ofthe constituent ingredients in a microencapsulated form, as describedin, e.g., JP-A-2001-277740 and JP-A-2001-277742. In the microcapsuletype image-recording layer, the constituent ingredients may be containedalso outside the microcapsules. A preferred embodiment of themicrocapsule type image-recording layer contains hydrophobic constituentingredients in microcapsules and contains hydrophilic constituentingredients outside the microcapsules. For obtaining better on-pressdevelopability, it is preferred to form the image-recording layer as amicrocapsule type image-recording layer.

For microencapsulating ingredients for constituting the image-recordinglayer, known methods can be used. Examples of processes for microcapsuleproduction include: the method utilizing coacervation as described inU.S. Pat. Nos. 2,800,457 and 2,800,458; the method based on interfacialpolymerization as described in U.S. Pat. No. 3,287,154, JP-B-38-19574,and JP-B-42-446; the method based on polymer deposition as described inU.S. Pat. Nos. 3,418,250 and 3,660,304; the method using anisocyanate/polyol wall material as described in U.S. Pat. No. 3,796,669;the method using an isocyanate wall material as described in U.S. Pat.No. 3,914,511; the method using a urea-formaldehyde orurea-formaldehyde-resorcinol wall-forming material as described in U.S.Pat. Nos. 4,001,140, 4,087,376, and 4,089,802; the method using a wallmaterial such as a melamine-formaldehyde resin or hydroxycellulose asdescribed in U.S. Pat. No. 4,025,445; the in-situ method based onmonomer polymerization as described in JP-B-36-9163 and JP-B-51-9079;the spray drying method as described in British Patent No. 930,422 andU.S. Pat. No. 3,111,407; and the electrolytic dispersion/cooling methodas described in British Patents Nos. 952,807 and 967,074. However,usable methods for microencapsulation should not be construed as beinglimited to these examples.

Preferred microcapsule walls for use in the invention havethree-dimensional crosslinks and have the property of swelling withsolvents. From this standpoint, preferred materials of microcapsulewalls are polyureas, polyurethanes, polyesters, polycarbonates,polyamides, and mixtures thereof. Especially preferred are polyureas andpolyurethanes. A compound having a crosslinkable functional groupcapable of being incorporated into the binder polymer, such as, e.g., anethylenically unsaturated bond, may be incorporated into microcapsulewalls.

The average particle diameter of the microcapsules is preferably0.01-3.0 μm, more preferably 0.05-2.0 μm, especially preferably 0.10-1.0μm. When the average microcapsule diameter is within this range,satisfactory resolution and long-term stability are obtained.

<Other Components of Image-Recording Layer>

Various compounds can be further incorporated into the image-recordinglayer in the invention according to need. Such optional ingredients willbe explained below.

<Surfactant>

A surfactant is preferably used for the image-recording layer in theinvention in order to enhance on-press developability in printinginitiation and to improve the state of coating surface. Examples of thesurfactant include nonionic surfactants, anionic surfactants, cationicsurfactants, amphoteric surfactants, and fluorochemical surfactants.Such surfactants may be used alone or in combination of two or morethereof.

The nonionic surfactants for use in the invention are not particularlylimited, and known ones can be used. Examples thereof includepolyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers,polyoxyethylene-polystyryl phenyl ethers,polyoxyethylene-polyoxypropylene alkyl ethers, partial fatty acid estersof glycerol, partial fatty acid esters of sorbitan, partial fatty acidesters of pentaerythritol, monoesters of fatty acids with propyleneglycol, partial fatty acid esters of sucrose, partial fatty acid estersof polyoxyethylene-sorbitan, partial fatty acid esters ofpolyoxyethylene-sorbitol, polyethylene glycol/fatty acid esters, partialfatty acid esters of polyglycerol, polyoxyethylated castor oils, partialfatty acid esters of polyoxyethylene-glycerol, fatty aciddiethanolamides, N,N-bis-2-hydroxyalkylamines, polyoxyethylenealkylamines, triethanolamine/fatty acid esters, trialkylamine oxides,polyethylene glycol, and copolymers of polyethylene glycol andpolypropylene glycol.

The anionic surfactants for use in the invention are not particularlylimited, and known ones can be used. Examples thereof include fatty acidsalts, abietic acid salts, hydroxyalkanesulfonic acid salts,alkanesulfonic acid salts, dialkylsulfosuccinic acid salts, (linearalkyl)benzenesulfonic acid salts, (branched alkyl)benzenesulfonic acidsalts, alkylnaphthalenesulfonic acid salts,alkylphenoxypolyoxyethylenepropylsulfonic acid salts, polyoxyethylenealkylsulfophenyl ether salts, N-methyl-N-oleyltaurine sodium salt,N-alkylsulfosuccinic acid monoamide disodium salts, petroleumsulfonicacid salts, sulfonated tallow oil, sulfuric acid ester salts of fattyacid alkyl esters, alkylsulfuric acid ester salts, polyoxyethylene alkylether sulfuric acid ester salts, fatty acid monoglyceride sulfuric acidester salts, polyoxyethylene alkylphenyl ether sulfuric acid estersalts, polyoxyethylene styrylphenyl ether sulfuric acid ester salts,alkylphosphoric acid ester salts, polyoxyethylene alkyl ether phosphoricacid ester salts, polyoxyethylene alkylphenyl ether phosphoric acidester salts, partially saponified styrene/maleic anhydride copolymers,partially saponified olefin/maleic anhydride copolymers, andnaphthalenesulfonic acid salt/formalin condensates.

The cationic surfactants for use in the invention are not particularlylimited, and known ones can be used. Examples thereof include alkylaminesalts, quaternary ammonium salts, polyoxyethylene alkylamine salts, andpolyethylene polyamine derivatives.

The amphoteric surfactants for use in the invention are not particularlylimited, and known ones can be used. Examples thereof includecarboxybetaines, aminocarboxylic acids, sulfobetaines, aminosulfuricacid esters, and imidazoline compounds.

In the surfactant names enumerated above, the term “polyoxyethylene” canbe replaced by “polyoxyalkylene” such as polyoxymethylene,polyoxypropylene, or polyoxybutylene. These surfactants also can be usedin the invention.

Other preferred examples of the surfactant include fluorochemicalsurfactants having a perfluoroalkyl group in the molecule. Examples ofsuch fluorochemical surfactants include anionic ones such asperfluoroalkanecarboxylic acid salts, perfluoroalkanesulfonic acidsalts, and perfluoroalkylphosphoric acid esters; amphoteric ones such asperfluoroalkyl betaines; cationic ones such asperfluoroalkyltrimethylammonium salts; and nonionic ones such asperfluoroalkylamine oxides, perfluoroalkyl ethylene oxide adducts,oligomers having a perfluoroalkyl group and a hydrophilic group,oligomers having a perfluoroalkyl group and an oleophilic group,oligomers having a perfluoroalkyl group, hydrophilic group, andoleophilic group, and urethanes having a perfluoroalkyl group and anoleophilic group. Furthermore, the fluorochemical surfactants describedin JP-A-62-170950, JP-A-62-226143, and JP-A-60-168144 are alsopreferred.

Surfactants can be used alone or in combination of two or more thereof.

The content of the surfactant is preferably 0.001-10% by mass, morepreferably 0.01-5% by mass, based on all solid components of theimage-recording layer.

<Colorant>

Besides the ingredients described above, other various compounds may beadded in the invention according to need. For example, a dye showingintense absorption in the visible light region can be used as a colorantfor images. Examples thereof include Oil Yellow #101, Oil Yellow #103,Oil Pink #312, Oil Green BG, Oil Blue BOS, Oil Blue #603, Oil Black BY,Oil Black BS, and Oil Black T-505 (all manufactured by Orient ChemicalIndustries Ltd.), Victoria Pure Blue, Crystal Violet (CI 42555), MethylViolet (CI 42535), Ethyl Violet, Rhodamine B (CI 145170B), MalachiteGreen (CI 42000), Methylene Blue (CI 52015), and the dyes shown inJP-A-62-293247. Furthermore, pigments such as phthalocyanine pigments,azo pigments, carbon black, and titanium oxide can also beadvantageously used.

When those colorants are used, the image areas formed through imageformation are easily distinguishable from the nonimage areas. There arehence cases where such a colorant is added as an auxiliary ingredient.The amount of the colorant to be added may be 0.01-10% by mass based onall solid components of the image-recording materials.

<Printing-Out Agent>

A compound which changes in color by the action of an acid or radicalcan be added to the image-recording layer in the invention in order toform a print-out image. As this compound can be effectively used variousdyes such as, e.g., diphenylmethane, triphenylmethane, thiazine,oxazine, xanthene, anthraquinone, iminoquninone, azo, and azomethinedyes.

Examples thereof include dyes such as Brilliant Green, Ethyl Violet,Methyl Green, Crystal Violet, Basic Fuchsine, Methyl Violet 2B,Quinaldine Red, Rose Bengal, Metanil Yellow, Thymolsulfophthalein,Xylenol Blue, Methyl Orange, Paramethyl Red, Congo Red, Benzopurpurine4B, α-Naphthyl Red, Nile Blue 2B, Nile Blue A, Methyl Violet, MalachiteGreen, Parafuchsine, Victoria Pure Blue BOH (manufactured by HodogayaChemical Co., Ltd.), Oil Blue #603 (manufactured by Orient ChemicalIndustries Ltd.), Oil Pink #312 (manufactured by Orient ChemicalIndustries Ltd.), Oil Red 5B (manufactured by Orient Chemical IndustriesLtd.), Oil Scarlet #308 (manufactured by Orient Chemical IndustriesLtd.), Oil Red OG (manufactured by Orient Chemical Industries Ltd.), OilRed RR (manufactured by Orient Chemical Industries Ltd.), Oil Green #502(manufactured by Orient Chemical Industries Ltd.), Spilon Red BEHSpecial (manufactured by Hodogaya Chemical Co., Ltd.), m-Cresol Purple,Cresol Red, Rhodamine B, Rhodamine 6G, Sulfo Rhodamine B, Auramine,4-p-diethylaminophenyliminonaphthoquinone,2-carboxyanilino-4-p-diethylaminophenyliminonaphthoquinone,2-carboxystearylamino-4-p-N,N-bis(hydroxyethyl)aminophenyliminonaphthoquinone,1-phenyl-3-methyl-4-p-diethylaminophenylimino-5-pyrazolone, and1-β-naphthyl-4-p-diethylaminophenylimino-5-pyrazolone and leuco dyessuch as p,p′,p″-hexamethyltriaminotriphenylmethane (Leuco CrystalViolet) and Pergascript Blue SRB (manufactured by Ciba-Geigy Ltd.).

Besides those, the leuco dyes known as materials for heat-sensitivepapers or pressure-sensitive papers are included in preferred examples.Specifically, examples thereof include crystal violet lactone, malachitegreen lactone, benzoyl leuco methylene blue,2-(N-phenyl-N-methylamino)-6-(N-p-tolyl-N-ethyl)aminofluoran,2-anilino-3-methyl-6-(N-ethyl-p-toluidino)fluoran, 3,6-dimethoxyfluoran,3-(N,N-diethylamino)-5-methyl-7-(N,N-dibenzylamino)fluoran,3-(N-cyclohexyl-N-methylamino)-6-methyl-7-anilinofluoran,3-(N,N-diethylamino)-6-methyl-7-anilinofluoran,3-(N,N-diethylamino)-6-methyl-7-xylidinofluoran,3-(N,N-diethylamino)-6-methyl-7-chlorofluoran,3-(N,N-diethylamino)-6-methoxy-7-aminofluoran,3-(N,N-diethylamino)-7-(4-chloroanilino)fluoran,3-(N,N-diethylamino)-7-chlorofluoran,3-(N,N-diethylamino)-7-benzylaminofluoran,3-(N,N-diethylamino)-7,8-benzofluoran,3-(N,N-dibutylamino)-6-methyl-7-anilinofluoran,3-(N,N-dibutylamino)-6-methyl-7-xylidinofluoran,3-piperidino-6-methyl-7-anilinofluoran,3-pyrrolidino-6-methyl-7-anilinofluoran,3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide,3,3-bis(1-n-butyl-2-methylindol-3-yl)phthalide,3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide,3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide,and 3-(4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide.

The dye changing in color by the action of an acid or radical may beadded to the image-recording layer in an amount of preferably 0.01-10%by mass based on the solid components of the layer.

<Polymerization Inhibitor>

A polymerization inhibitor is preferably added in a small amount to theimage-recording layer in the invention in order to prevent thepolymerizable compound from unnecessarily undergoing heat polymerizationduring the production or storage of the image-recording layer.

Preferred examples of the heat polymerization inhibitor includehydroquinone, p-methoxyphenol, di-t-butyl-p-cresol, pyrogallol,t-butylcatechol, benzoquinone, 4,4′-thiobis(3-methyl-6-t-butylphenol),2,2′-methylenebis(4-methyl-6-t-butylphenol), andN-nitroso-N-phenylhydroxylamine aluminum salt.

The amount of the heat polymerization inhibitor is preferably about0.01-5% by mass based on all solid components of the image-recordinglayer.

<Higher Fatty Acid Compound>

A higher fatty acid or a derivative thereof, such as behenic acid orbehenamide, may be added to the image-recording layer in the inventionso as to become present in a higher concentration in the image-recordinglayer surface during drying after coating, for the purpose of preventingthe polymerization inhibition caused by oxygen. The amount of the higherfatty acid or derivative thereof to be added is preferably about from0.1 to 10% by mass based on all solid components of the image-recordinglayer.

<Plasticizer>

The image-recording layer in the invention may contain a plasticizer soas to have improved on-press developability.

Examples of the plasticizer include phthalic esters such as dimethylphthalate, diethyl phthalate, dibutyl phthalate, diisobutyl phthalate,dioctyl phthalate, octyl capryl phthalate, dicyclohexyl phthalate,ditridecyl phthalate, butyl benzyl phthalate, diisodecyl phthalate, anddiallyl phthalate; glycol esters such as dimethyl glycol phthalate,ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butylphthalyl butyl glycolate, and triethylene glycol dicaprylate; phosphoricesters such as tricresyl phosphate and triphenyl phosphate; aliphaticdibasic acid esters such as diisobutyl adipate, dioctyl adipate,dimethyl sebacate, dibutyl sebacate, dioctyl azelate, and dibutylmaleate; and poly(glycidyl methacrylate), triethyl citrate, glyceroltriacetyl ester, and butyl laurate.

The content of the plasticizer in the image-recording layer ispreferably up to about 30% by mass based on all solid components of theimage-recording layer.

<Fine Inorganic Particles>

The image-recording layer in the invention may contain fine inorganicparticles for the purposes of improving cured-film strength in imageareas and improving the removability of nonimage areas in on-pressdevelopment.

Preferred examples of the fine inorganic particles include silica,alumina, magnesium oxide, titanium oxide, magnesium carbonate, calciumalginate, and mixtures thereof. Even though these particulate materialsdo not have the property of converting light to heat, they can be usedfor strengthening the film, enhancing interfacial adhesion by surfaceroughening, etc.

Such fine inorganic particles have an average particle diameter ofpreferably from 5 nm to 10 μm, more preferably 0.5-3 μm. When the fineinorganic particles have an average particle diameter within that range,the particles are stably dispersed in the image-recording layer toenable the image-recording layer to retain sufficient film strength andgive nonimage areas which have excellent hydrophilicity and are lesssusceptible to scumming during printing.

The fine inorganic particles described above are easily available ascommercial products, e.g., colloidal silica dispersions.

The content of the fine inorganic particles is preferably 40% by mass orlower, more preferably 30% by mass or lower, based on all solidcomponents of the image-recording layer.

<Low-Molecular Hydrophilic Compound>

The image-recording layer in the invention may contain a hydrophiliclow-molecular compound so as to have improved on-press developability.Examples of the hydrophilic low-molecular compound include the followingwater-soluble organic compounds: glycols such as ethylene glycol,diethylene glycol, triethylene glycol, propylene glycol, dipropyleneglycol, and tripropylene glycol and ether or ester derivatives of these;polyhydroxy compounds such as glycerol and pentaerythritol; organicamines such as triethanolamine, diethanolamine, and monoethanolamine andsalts of these; organic sulfonic acids such as toluenesulfonic acid andbenzenesulfonic acid and salts of these; organic phosphonic acids suchas phenylphosphonic acid and salts thereof; and organic carboxylic acidssuch as tartaric acid, oxalic acid, citric acid, malic acid, lacticacid, gluconic acid, and amino acids and salts of these.

<Formation of Image-Recording Layer]

The image-recording layer in the invention is formed by dispersing ordissolving the necessary ingredients in a solvent to prepare a coatingfluid and applying the coating fluid. Examples of the solvent to be usedhere include ethylene dichloride, cyclohexanone, methyl ethyl ketone,methanol, ethanol, propanol, ethylene glycol monomethyl ether,1-methoxy-2-propanol, 2-methyoxyethyl acetate, 1-methoxy-2-propylacetate, dimethoxyethane, methyl lactate, ethyl lactate,N,N-dimethylacetamide, N,N-dimethylformamide, tetramethylurea,N-methylpyrrolidone, dimethyl sulfoxide, sulfolane, γ-butyrolactone,toluene, and water. However, the solvent should not be construed asbeing limited to these examples. These solvents may be used alone or asa mixture thereof. The solid concentration of the coating fluid ispreferably 1-50% by mass.

It is also possible to form the image-recording layer according to theinvention by dispersing or dissolving the same or different ingredientsdescribed above in the same or different solvents to prepare two or morecoating fluids and repeatedly conducting application and dryingoperations.

The amount of the image-recording layer (on a dry basis) to be obtainedon the support through application and drying varies depending on uses.In general, however, the amount thereof is preferably 0.3-3.0 g/m². Whenthe image-recording layer amount is within this range, theimage-recording layer has satisfactory sensitivity and satisfactory filmproperties.

For applying the coating fluid, various methods can be used. Examplesthereof include bar coater coating, spin coating, spray coating, curtaincoating, dip coating, air knife coating, blade coating, and rollcoating.

[Protective Layer]

In the lithographic printing plate precursor of the invention, aprotective layer can be formed according to need on the image-recordinglayer for the purposes of preventing the image-recording layer fromsuffering mars, shutting off oxygen, and preventing ablation inhigh-illuminance laser exposure.

In the invention, exposure is usually conducted in the air. Theprotective layer serves to prevent low-molecular compounds present inthe air, such as, e.g., oxygen and basic substances, which inhibit theimage-forming reaction caused in the image-recording layer by exposure,from coming into the image-recording layer to thereby prevent theimage-forming reaction from being inhibited by exposure in the air.Consequently, the protective layer is desired to have the followingproperties: to have low permeability to low-molecular compoundsincluding oxygen; to satisfactorily transmit the light to be used forexposure; to have excellent adhesion to the image-recording layer; andto be capable of being easily removed in an on-press development stepafter exposure. Various investigations have hitherto been made onprotective layers having such properties. Such protective layers aredescribed in detail in, e.g., U.S. Pat. No. 3,458,311 and JP-B-55-49729.

Examples of materials for the protective layer include water-solublepolymeric compounds having relatively excellent crystallinity. Specificexamples thereof include water-soluble polymers such as poly(vinylalcohol), polyvinylpyrrolidone, acid celluloses, gelatin, gum arabic,and poly(acrylic acid). Of these, poly(vinyl alcohol) (PVA), when usedas the main component, gives most satisfactory results concerning basicproperties such as oxygen barrier properties and removability indevelopment. As long as the poly(vinyl alcohol) contains unsubstitutedvinyl alcohol units, which impart the oxygen barrier properties andwater solubility required of the protective layer, it may be one whichhas been partly substituted with an ester, ether, or acetal or may beone which partly has other comonomer units.

Examples of the poly(vinyl alcohol) include ones having a degree ofhydrolysis of 71-100% by mole and a degree of polymerization in therange of 300-2,400. Specific examples thereof include PVA-105, PVA-110,PVA-117, PVA-117H, PVA-120, PVA-124, PVA-124H, PVA-CS, PVA-CST, PVA-HC,PVA-203, PVA-204, PVA-205, PVA-210, PVA-217, PVA-220, PVA-224,PVA-217EE, PVA-217E, PVA-220E, PVA-224E, PVA-405, PVA-420, PVA-613, andL-8, manufactured by Kuraray Co., Ltd.

Ingredients for the protective layer (selection of PVA, use ofadditives, etc.), the amount of the layer to be formed by coating, etc.are suitably selected while taking account of susceptibility to fogging,adhesion, marring resistance, and the like besides oxygen barrierproperties and removability in development. In general, the higher thedegree of hydrolysis of the PVA (i.e., the higher the content ofunsubstituted vinyl alcohol units in the protective layer) and thelarger the film thickness, the higher the oxygen barrier properties andthe more the protective layer is preferred from the standpoint ofsensitivity. Furthermore, it is preferred to regulate oxygen barrierproperties so as not to be too high, in order to prevent an unnecessarypolymerization reaction from occurring during production and storage andto prevent undesirable fogging, line thickening, or the like inimagewise exposure. Consequently, the oxygen permeability A as measuredat 25° C. and 1 atm preferably satisfies 0.2<A<20 (mL/m²·day).

It is preferred that an inorganic layer compound such as, e.g., thatdescribed in JP-A-11-38633 be incorporated into the protective layer inthe invention. By using an inorganic layer compound in combination withthe binder, satisfactory oxygen barrier properties can be obtained.

The inorganic layer compound to be used in the invention is in the formof particles each having a thin platy shape. Examples thereof includemicas such as natural and synthetic micas represented by the formulaA(B,C)₂₋₅D₄O₁₀(OH,F,O)₂ [wherein A is any of K, Na, and Ca; B and C eachare any of Fe(II), Fe(III), Mn, Al, Mg, and V; and D is Si or Al], talcrepresented by the formula 3MgO.4SiO.H₂O taeniolite, montmorillonite,saponite, hectorite, and zirconium phosphate.

Of the micas, examples of the natural micas include commonmica,paragonite, phlogopite, biotite, and lepidolite. Examples of thesynthetic micas include nonswelling micas such as fluorophlogopiteKMg₃(AlSi₃O₁₀)F₂ and potassium tetrasilicic mica KMg₂₅(Si₄O₁₀)F₂ andswelling micas such as sodium tetrasilicic mica NaMg_(2.5)(SiO₄O₁₀)F₂,sodium or lithium taeniolite (Na,Li)Mg₂Li(Si₄O₁₀)F₂, and montmorillonitetype sodium or lithium hectorite(Na,Li)_(1/8)Mg_(2/5)Li_(1/8)(Si₄O₁₀)F₂. Synthetic smectite also isuseful.

Of those inorganic layer compounds, the fluorinated swelling micas,which are synthetic inorganic layer compounds, are especially useful inthe invention.

The shape of the inorganic layer compound to be used in the invention isas follows from the standpoint of controlling diffusion. The smaller thethickness thereof, the better. With respect to the planar size thereof,larger sizes are preferred as long as the layer compound impairs neitherthe flatness of the coating surface nor the transmission of actinicrays. Consequently, the aspect ratio thereof may be 20 or higher and ispreferably 100 or higher, especially preferably 200 or higher. Theaspect ratio of a particle is the ratio of the major-axis length to thethickness of the particle, and can be determined from projected imageson photomicrographs of the particle. The higher the aspect ratio, thehigher the effect obtained.

The particle diameter of the inorganic layer compound to be used in theinvention may be 0.3-20 μm and is preferably 0.5-10 μm, especiallypreferably 1-5 μm, in terms of average major-axis length. The averagethickness of the particles may be 0.1 μm or smaller and is preferably0.05 μm or smaller, especially preferably 0.01 μm or smaller. Forexample, swelling synthetic micas, which are typical of inorganic layercompounds, have thicknesses of about 1-50 nm and planar sizes of about1-20 μm.

The incorporation of such particles of an inorganic layer compoundhaving a high aspect ratio in the protective layer improves coating filmstrength and can effectively prevent the permeation of oxygen andmoisture. The layer compound hence prevents the protective layer fromdeteriorating through deformation, etc.

The amount of the inorganic layer compound to be contained in theprotective layer may be 5-55% by mass based on all solid components ofthe protective layer. Preferably, the amount thereof is 1-40% by mass.In case where the amount of the compound is smaller than 5% by mass, theincorporation of the compound is ineffective in improving adhesion. Incase where the amount thereof exceeds 55% by mass, coating filmformation becomes insufficient, resulting in reduced sensitivity. Whentwo or more inorganic layer compounds are used in combination, it ispreferred that the sum of these inorganic layer compounds in terms of %by mass be within that range.

Other ingredients for the protective layer include the following.Glycerol, dipropylene glycol, or the like may be added in an amount ofseveral percents by mass based on the (co)polymer to impart flexibility.Furthermore, an anionic surfactant such as a sodium alkyl sulfate orsodium alkylsulfonate, an amphoteric surfactant such as analkylaminocarboxylic acid salt or alkylaminodicarboxylic acid salt, or anonionic surfactant such as a polyoxyethylene alkylphenyl ether can beadded in an amount of several percents by mass based on the (co)polymer.

The thickness of the protective layer is preferably 0.05-4 μm,especially preferably 0.1-2.5 μm.

The adhesion of the protective layer to the image areas and the marringresistance or the like of the protective layer are also significantlyimportant in the handling of the lithographic printing plate precursor.This is because when a protective layer which comprises a water-solublepolymeric compound and is hence hydrophilic is superposed on theimage-recording layer, which is hydrophobic, then the protective layeris apt to peel off due to insufficient adhesive force. There are caseswhere defects such as, e.g., film cure failures caused by polymerizationinhibition by oxygen are developed in the areas from which theprotective layer has peeled off.

Various proposals have been made on improvements of adhesion between animage-recording layer and a protective layer to eliminate such failures.For example, JP-A-49-70702 describes a technique in which a hydrophilicpolymer consisting mainly of poly(vinyl alcohol) is mixed with 20 to 60%by mass acrylic emulsion, water-insoluble vinylpyrrolidone/vinyl acetatecopolymer, or the like and this mixture is applied to an image-recordinglayer to form a layer thereon to thereby obtain sufficient adhesion. Anyof such known techniques can be used in the invention. Coating methodsfor protective layer formation are described in detail in, e.g., U.S.Pat. No. 3,458,311 and JP-B-55-49729.

Other functions can be imparted to the protective layer. For example, acolorant which highly transmits infrared rays to be used for exposureand is capable of efficiently absorbing light having other wavelengths(e.g., a water-soluble dye) is added to thereby improve suitability forhandling in safelight without causing a decrease in sensitivity.

[Support]

The support to be used in the lithographic printing plate precursor ofthe invention is not particularly limited as long as it is a platymaterial having dimensional stability. Examples thereof include paper,paper laminated with a plastic (e.g., polyethylene, polypropylene, orpolystyrene), metal sheets (e.g., aluminum, zinc, and copper), plasticfilms (e.g., cellulose diacetate, cellulose triacetate, cellulosepropionate, cellulose butyrate, cellulose acetate butyrate, cellulosenitrate, poly(ethylene terephthalate), polyethylene, polystyrene,polypropylene, polycarbonates, and poly(vinyl acetal)), and paper orplastic films to which any of those metals has been laminated orvapor-deposited. Preferred examples of the support include polyesterfilms and aluminum sheets. Of these, aluminum sheets are preferredbecause they have satisfactory dimensional stability and are relativelyinexpensive.

The aluminum sheets are sheets of pure aluminum, sheets of an alloy ofaluminum as the main component with a slight amount of one or more otherelements, or ones comprising a thin film of aluminum or an aluminumalloy and a plastic laminated thereto. Examples of the non-aluminumelements contained in the aluminum alloy include silicon, iron,manganese, copper, magnesium, chromium, zinc, bismuth, nickel, andtitanium. The content of such non-aluminum elements in the alloy ispreferably up to 10% by mass. Although a sheet of pure aluminum ispreferred in the invention, an aluminum sheet containing a slight amountof non-aluminum elements may be used because completely pure aluminum isdifficult to produce by the current refining technology.

The aluminum sheet to be used is not limited in composition and can besuitably selected from sheets of known aluminum materials in generaluse.

The thickness of the support is preferably 0.1-0.6 mm, more preferably0.15-0.4 mm.

Before being used, the aluminum sheet is preferably subjected to asurface treatment such as a surface-roughening treatment or anodizationtreatment. Such a surface treatment facilitates the attainment ofimproved hydrophilicity and adhesion between an image-recording layerand the support. Before being subjected to a surface-rougheningtreatment, the aluminum sheet may be degreased according to need with asurfactant, organic solvent, alkaline aqueous solution, or the like toremove a rolling oil remaining on the surface thereof.

The surface-roughening treatment of the aluminum sheet may be conductedby various methods. Examples thereof include mechanicalsurface-roughening treatment, electrochemical surface-rougheningtreatment (surface-roughening treatment in which a surface layer iselectrochemically dissolved away), and chemical surface-rougheningtreatment (surface-roughening treatment in which the surface isselectively dissolved away chemically).

For the mechanical surface-roughening treatment, known techniques can beused, such as ball polishing, brushing, blasting, and buffing.Furthermore, use may be made of a transfer method in which a roll havingsurface irregularities is used in an aluminum rolling step to transferthe irregularities to the aluminum sheet.

Examples of techniques for the electrochemical surface-rougheningtreatment include a method in which the aluminum sheet is treated in anelectrolytic solution containing an acid, e.g., hydrochloric acid ornitric acid, while applying an alternating or direct current thereto.Examples thereof further include the method using a mixed acid asdescribed in JP-A-54-63902.

The aluminum sheet which has undergone a surface-roughening treatment issubjected according to need to an alkali etching treatment with anaqueous solution of potassium hydroxide, sodium hydroxide, or the likeand then to a neutralization treatment. Thereafter, the aluminum sheetmay be subjected to an anodization treatment for enhancing wearingresistance according to need.

For the anodization treatment of the aluminum sheet, variouselectrolytes which enable the formation of a porous oxide film can beused. In general, sulfuric acid, hydrochloric acid, oxalic acid, chromicacid, or a mixture of two or more of these acids is used. Theconcentration of any of these electrolytes is suitably determinedaccording to the kind of the electrolyte.

Conditions for the anodization treatment cannot be unconditionallyspecified because they vary over a wide range depending on theelectrolyte to be used. In general, however, the conditions preferablyinclude an electrolyte concentration in the solution of 1-80% by mass,solution temperature of 5-70° C., current density of 5-60 A/dm², voltageof 1-100 V, and electrolysis period of from 10 seconds to 5 minutes. Theamount of the film to be formed by anodization is preferably 1.0-5.0g/m², more preferably 1.5-4.0 g/m². When the amount of the film iswithin this range, satisfactory printing durability and the satisfactorymarring resistance of nonimage areas of the lithographic printing plateare obtained.

The support to be used in the invention may be one which has undergone asurface treatment such as those shown above and has an anodized coating.Although this substrate may be used as it is, suitably selectedtreatments can be conducted according to need for the purpose of furtherimproving adhesion to an upper layer, hydrophilicity, unsusceptibilityto scumming, heat-insulating properties, etc. Examples of suchtreatments include the treatment for enlarging or filling micropores ofan anodized coating as described in JP-A-2001-253181 andJP-A-2001-322365 and a surface-hydrophilizing treatment in which thesupport is immersed in an aqueous solution containing a hydrophiliccompound. It is a matter of course that the pore-enlarging treatment andpore-filling treatment are not limited to those described in thedocuments, and any of known methods can be used.

For example, the pore-filling treatment can be conducted not only bypore filling with a vapor but also by a treatment with fluorozirconicacid alone, treatment with sodium fluoride, or pore filling with a vaporcontaining lithium chloride.

The pore-filling treatment to be used in the invention is notparticularly limited and known methods can be used. Preferred of theseare a pore-filling treatment with an aqueous solution containing aninorganic fluorine compound, a pore-filling treatment with water vapor,and a pore-filling treatment with hot water. These methods will beexplained below.

Preferred examples of the inorganic fluorine compound to be used in thepore-filling treatment with an aqueous solution containing an inorganicfluorine compound include metal fluorides.

Specific examples thereof include sodium fluoride, potassium fluoride,calcium fluoride, magnesium fluoride, sodium fluorozirconate, potassiumfluorozirconate, sodium fluorotitanate, potassium fluorotitanate,ammonium fluorozirconate, ammonium fluorotitanate, potassiumfluorotitanate, fluorozirconic acid, fluorotitanic acid,hexafluorosilicic acid, nickel fluoride, iron fluoride, fluorophosphoricacid, and ammonium fluorophosphate. Preferred of these are sodiumfluorozirconate, sodium fluorotitanate, fluorozirconic acid, andfluorotitanic acid.

The concentration of the inorganic fluorine compound in the aqueoussolution is preferably 0.01% by mass or higher, more preferably 0.05% bymass or higher, from the standpoint of sufficiently filling microporesof the anodized coating, and is preferably 1% by mass or lower, morepreferably 0.5% by mass or lower, from the standpoint ofunsusceptibility to scumming.

The aqueous solution containing an inorganic fluorine compoundpreferably further contains a phosphoric acid salt compound. Use of theaqueous solution containing a phosphoric acid salt compound improves thehydrophilicity of the surface of the anodized coating and, hence,on-press developability and unsusceptibility to scumming can beimproved.

Preferred examples of the phosphoric acid salt compound includephosphates of metals such as alkali metals and alkaline earth metals.

Specific examples thereof include zinc phosphate, aluminum phosphate,ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogenphosphate, monoammonium phosphate, monopotassium phosphate, monosodiumphosphate, potassium dihydrogen phosphate, dipotassium hydrogenphosphate, calcium phosphate, sodium ammonium hydrogen phosphate,magnesium hydrogen phosphate, magnesium phosphate, ferrous phosphate,ferric phosphate, sodium dihydrogen phosphate, sodium phosphate,disodium hydrogen phosphate, lead phosphate, diammonium phosphate,calcium dihydrogen phosphate, lithium phosphate, phosphotungstic acid,ammonium phosphotungstate, sodium phosphotungstate, ammoniumphosphomolybdate, sodium phosphomolybdate, sodium phosphite, sodiumtripolyphosphate, and sodium pyrophosphate. Preferred of these aresodium dihydrogen phosphate, disodium hydrogen phosphate, potassiumdihydrogen phosphate, and dipotassium hydrogen phosphate.

Inorganic fluorine compound/phosphoric acid salt compound combinationsare not particularly limited. It is, however, preferred that the aqueoussolution should contain at least sodium fluorozirconate as the inorganicfluorine compound and further contain at least sodium dihydrogenphosphate as the phosphoric acid salt compound.

The concentration of the phosphoric acid salt compound in the aqueoussolution is preferably 0.01% by mass or higher, more preferably 0.1% bymass or higher, from the standpoint of on-press developability andunsusceptibility to scumming, and is preferably 20% by mass or lower,more preferably 5% by mass or lower, from the standpoint of solubility.

Proportions of the compounds in the aqueous solution are notparticularly limited. However, the ratio of the amount by mass of theinorganic fluorine compound to that of the phosphoric acid salt compoundis preferably from 1/200 to 10/1, more preferably from 1/30 to 2/1.

The temperature of the aqueous solution is preferably 20° C. or higher,more preferably 40° C. or higher, and is preferably 100° C. or lower,more preferably 80° C. or lower.

The pH of the aqueous solution is preferably 1 or higher, morepreferably 2 or higher, and is preferably 11 or lower, more preferably 5or lower.

Methods for the pore-filling treatment with an aqueous solutioncontaining an inorganic fluorine compound are not particularly limited.Examples thereof include the immersion method and spraying method. Anyone of such methods may be used alone to conduct the treatment once ortwo or more times. Alternatively, two or more of such methods may beused in combination.

Preferred of these is the immersion method. In the case of using theimmersion method to conduct the treatment, the treatment time ispreferably 1 second or longer, more preferably 3 seconds or longer, andis preferably 100 seconds or shorter, more preferably 20 seconds orshorter.

Examples of the pore-filling treatment with water vapor include a methodin which elevated- or ordinary-pressure water vapor is continuously ordiscontinuously brought into contact with the anodized coating.

The temperature of the water vapor is preferably 80° C. or higher, morepreferably 95° C. or higher, and is preferably 105° C. or lower.

The pressure of the water vapor is preferably in the range of from[(atmospheric pressure)−50 mmAg] to [(atmospheric pressure)+300 mmAq](1.008×10⁵-1.043×10⁵ Pa).

The time period in which water vapor is contacted is preferably 1 secondor longer, more preferably 3 seconds or longer, and is preferably 100seconds or shorter, more preferably 20 seconds or shorter.

Examples of the pore-filling treatment with hot water include a methodin which the aluminum plate having an anodized coating is immersed inhot water.

The hot water may contain an inorganic salt (e.g., phosphoric acid salt)or an organic salt. The temperature of the hot water is preferably 80°C. or higher, more preferably 95° C. or higher, and is preferably 100°C. or lower.

The time period in which the anodized coating is immersed in hot wateris preferably 1 second or longer, more preferably 3 seconds or longer,and is preferably 100 seconds or shorter, more preferably 20 seconds orshorter.

In the invention, a treatment for enlarging micropores of the anodizedcoating may be conducted, as described in JP-A-2001-322365, prior to thepore filling. Furthermore, a surface-hydrophilizing treatment may beperformed after the pore filling.

Examples of the hydrophilizing treatment include an alkali metalsilicate method such as those described in U.S. Pat. Nos. 2,714,066,3,181,461, 3,280,734, and 3,902,734. In this method, the support istreated by immersion or electrolysis in an aqueous solution of sodiumsilicate or the like. Other examples of the hydrophilizing treatmentinclude the method in which the support is treated with potassiumfluorozirconate as described in JP-B-36-22063 and the method in whichthe support is treated with poly(vinylphosphonic acid) as described inU.S. Pat. Nos. 3,276,868, 4,153,461, and 4,689,272.

In the case where a support having insufficient surface hydrophilicity,such as, e.g., a polyester film, is used as the support in theinvention, it is desirable to apply a hydrophilic layer thereto tohydrophilize the surface. The hydrophilic layer preferably is: thehydrophilic layer described in JP-A-2001-199175 formed by applying acoating fluid containing a colloid of an oxide or hydroxide of at leastone element selected from beryllium, magnesium, aluminum, silicon,titanium, boron, germanium, tin, zirconium, iron, vanadium, antimony,and transition metals; the hydrophilic layer described inJP-A-2002-79772 which has an organic hydrophilic matrix obtained by thecrosslinking or pseudocrosslinking of an organic hydrophilic polymer; ahydrophilic layer having an inorganic hydrophilic matrix obtained bysol-gel conversion comprising the hydrolysis/condensation reaction of apolyalkoxysilane, titanate, zirconate, or aluminate; or a hydrophiliclayer comprising a thin inorganic film having a surface comprising ametal oxide. Preferred of these is the hydrophilic layer formed byapplying a coating fluid containing a colloid of an oxide or hydroxideof silicon.

In the case of using a polyester film or the like as the support in theinvention, it is preferred to form an antistatic layer on thehydrophilic-layer side or opposite side of this support or on each side.When an antistatic layer is disposed between the support and thehydrophilic layer, it contributes also to an improvement in adhesionbetween the support and the hydrophilic layer. As the antistatic layercan be used, for example, the polymer layer described in JP-A-2002-79772which contains fine metal oxide particles or a matting agent dispersedtherein.

The support to be used in the invention preferably has a center-lineaverage surface roughness of 0.10-1.2 μm. When the surface roughnessthereof is within this range, then satisfactory adhesion to theimage-recording layer, satisfactory printing durability, andsatisfactory unsusceptibility to scumming are obtained.

[Back Coat Layer]

A back coat can be formed on the back side of the support according toneed after the support has undergone a surface treatment or after anundercoat layer has been formed.

Preferred examples of the back coat include a coating layer made of theorganic polymeric compound described in JP-A-5-45885 or of the metaloxide obtained by hydrolyzing and condensation-polymerizing anorganometallic compound or inorganic metal compound as described inJP-A-6-35174. Preferred of these materials are alkoxy compounds ofsilicon, such as Si(OCH₃)₄, Si(OC₂H₅)₄, Si(OC₃H₇)₄, and Si(OC₄H₉)₄. Thisis because starting materials for such silicon compounds are easilyavailable at low cost.

[Undercoat Layer]

In the lithographic printing plate precursor of the invention, anundercoat layer may be disposed between the image-recording layer andthe support according to need especially when the lithographic printingplate precursor is of the on-press development type. The undercoat layerserves to facilitate the removal of the image-recording layer from thesupport in unexposed areas and thereby improves on-press developability.Furthermore, in the case of exposure with an infrared laser, theundercoat layer functions as a heat-insulating layer, whereby the heatgenerated by the exposure does not diffuse to the support and isefficiently utilized. There is hence an advantage that sensitivity canbe heightened.

Preferred examples of the undercoat layer include the silane couplingagent having an addition-polymerizable, ethylenic double-bond reactivegroup described in JP-A-10-282679 and the phosphorus compound having anethylenic double-bond reactive group described in JP-A-2-304441.

Most preferred examples of the undercoat layer include a polymeric resinobtained by copolymerizing a monomer having an adsorbable group, amonomer having a hydrophilic group, and a monomer having a crosslinkablegroup.

An essential component of the polymeric undercoat is groups adsorbableonto hydrophilic support surfaces. Whether a compound has adsorbabilityonto hydrophilic support surfaces can be judged, for example, by thefollowing method.

The test compound is dissolved in a good solvent therefor to prepare acoating fluid. This coating fluid is applied to a support in an amountof 30 mg/m² on a dry basis and dried. Subsequently, the support coatedwith the test compound is sufficiently washed with the good solvent.Thereafter, the amount of the test compound remaining unremoved afterthe washing is determined to calculate the amount of the test compoundadsorbed to the support. In determining the residual compound amount,the compound amount may be directly determined or may be calculatedthrough the determination of the amount of the test compound dissolvedin the washings. The compound amount can be determined by, for example,fluorescent X-ray spectroscopy, reflection spectroscopy/absorptiometry,or liquid chromatography. A compound having adsorbability onto supportsis a compound which remains in an amount of 1 mg/m² or larger even afterthe washing treatment.

The groups adsorbable onto hydrophilic support surfaces are functionalgroups capable of forming a chemical bond (e.g., an ionic bond, hydrogenbond, coordination bond, or bond by intermolecular force) with asubstance (e.g., metal or metal oxide) or functional group (e.g.,hydroxyl group) present on the hydrophilic support surfaces. Theadsorbable groups preferably are acid groups or cationic groups.

The acid groups preferably have an acid dissociation constant (pK_(a))of 7 or lower. Examples of the acid groups include phenolic hydroxyl,carboxyl, —SO₃H, —OSO₃H, —PO₃H₂, —OPO₃H₂, —CONHSO₂—, —SO₂NHSO₂—, and—COCH₂COCH₃. Especially preferred are the phosphoric acid groups(—OPO₃H₂ and —PO₃H₂). These acid groups may be metal salts.

The cationic groups preferably are onium salts. Examples of the oniumsalts include ammonium, phosphonium, arsonium, stibonium, oxonium,sulfonium, selenonium, stannonium, and iodonium groups. Preferred areammonium, phosphonium, and sulfonium.

More preferred are ammonium and phosphonium. Most preferred is ammonium.

Especially preferred examples of the monomer having an adsorbable groupinclude compounds represented by the following formula (ii) or (iii).

In formula (ii), R¹, R², and R³ each independently represent a hydrogenatom, halogen atom, or alkyl group having 1-6 carbon atoms. R¹, R², andR³ each independently preferably represent a hydrogen atom or an alkylgroup having 1-6 carbon atoms, more preferably represent a hydrogen atomor an alkyl group having 1-3 carbon atoms, and most preferably representa hydrogen atom or methyl. R² and R³ especially preferably are hydrogenatoms.

In formula (ii), X is an oxygen atom (—O—) or imino (—NH—). X morepreferably is an oxygen atom. In formula (ii), L is a divalentconnecting group. L preferably is a divalent aliphatic group (alkylene,substituted alkylene, alkenylene, substituted alkenylene, alkynylene, orsubstituted alkynylene group), a divalent aromatic group (arylene orsubstituted arylene group), or a divalent heterocyclic group or is acombination of any of these groups with an oxygen atom (—O—), sulfuratom (—S—), imino (—NH—), substituted imino (—NR—, wherein R is analiphatic, aromatic, heterocyclic group), or carbonyl (—CO—).

The aliphatic group may have a cyclic structure or a branched structure.The number of carbon atoms in the aliphatic group is preferably 1-20,more preferably 1-15, most preferably 1-10. The aliphatic grouppreferably is a saturated aliphatic group rather than an unsaturatedaliphatic group. The aliphatic group may have one or more substituents.Examples of the substituents include halogen atoms, hydroxyl, aromaticgroups, and heterocyclic groups.

The number of carbon atoms in the aromatic group preferably is 6-20,more preferably 6-15, most preferably 6-10. The aromatic group may haveone or more substituents. Examples of the substituents include halogenatoms, hydroxyl, aliphatic groups, aromatic groups, and heterocyclicgroups.

The heterocyclic group preferably comprises a 5-membered or 6-memberedheterocycle. The heterocyclic group may comprise a heterocycle and,fused thereto, another heterocycle or an aliphatic or aromatic ring. Theheterocyclic group may have one or more substituents. Examples of thesubstituents include halogen atoms, hydroxyl, oxo (═O), thioxo (═S),imino (═NH), substituted imino (═N—R, wherein R is an aliphatic,aromatic, or heterocyclic group), aliphatic groups, aromatic groups, andheterocyclic groups.

L preferably is a divalent connecting group comprising two or morepolyoxyalkylene structures. More preferably, the polyoxyalkylenestructures are polyoxyethylene structures. In other words, it ispreferred that L comprise —(OCH₂CH₂)_(n)— (n is an integer of 2 orlarger).

In formula (ii), Z is a functional group capable of being adsorbed ontoa hydrophilic support surface. Y is a carbon atom or nitrogen atom. WhenY is a nitrogen atom and L is bonded to Y to form a quaternarypyridinium group, then Z is not essential because this group itself isadsorbable.

The adsorbable functional group is as described above.

Typical examples of the monomers represented by formula (ii) or (iii)are shown below.

Preferred examples of the hydrophilic groups of the polymeric resinusable for undercoating in the invention include hydroxyl, carboxyl,carboxylate, hydroxyethyl, polyoxyethyl, hydroxypropyl, polyoxypropyl,amino, aminoethyl, aminopropyl, ammonium, amide, carboxymethyl, sulfo,and phosphate groups. A monomer having any of these hydrophilic groupsand a polymerizable group is used as a comonomer ingredient for thepolymeric resin.

The polymeric resin for undercoating in the invention preferably hascrosslinkable groups. Crosslinkable groups improve adhesion to imageareas. For imparting crosslinkability to the polymeric resin forundercoating, use may be made of a method in which crosslinkablefunctional groups such as, e.g., ethylenically unsaturated bonds areincorporated into side chains of the polymer. Alternatively, a methodmay be used in which a compound which has a substituent having a chargeof the polarity opposite to that of the polar substituents of thepolymeric resin and further has an ethylenically unsaturated bond isused to form a salt structure and thereby impart crosslinkability.

Examples of polymers having ethylenically unsaturated bonds in sidechains of the molecule include a polymer which is a polymer of an esteror amide of acrylic or methacrylic acid and in which ester or amideresidues (R in —COOR or —CONHR) have an ethylenically unsaturated bond.

Examples of the residues (the R) having an ethylenically unsaturatedbond include —(CH₂)_(n)CR₁═CR₂R₃, —(CH₂O)_(n)CH₂CR₁═CR₂R₃,—(CH₂CH₂O)_(n)CH₂CR₁═CR₂R₃, —(CH₂)_(n)NH—CO—O—CH₂CR₁═CR₂R₃,—(CH₂)_(n)—O—CO—CR₁═CR₂R₃, and —(CH₂CH₂O)₂—X (wherein R₁ to R₃ eachrepresent a hydrogen atom, a halogen atom, or an alkyl, aryl, alkoxy, oraryloxy group having 1-20 carbon atoms, provided that R₁ may be bondedto R₂ or R₃ to form a ring; n represents an integer of 1-10; and Xrepresents a dicyclopentadienyl residue).

Examples of the ester residues include —CH₂CH═CH₂ (given inJP-B-7-21633), —CH₂CH₂O—CH₂CH═CH₂, —CH₂C(CH₃)═CH₂, —CH₂CH═CH—C₆H₅,—CH₂CH₂OCOCH═CH—C₆H₅, —CH₂CH₂NHCOO—CH₂CH═CH₂, and —CH₂CH₂O—X (wherein Xrepresents a dicyclopentadienyl residue).

Examples of the amide residues include —CH₂CH═CH₂, —CH₂CH₂O—Y (wherein Yrepresents a cyclohexene residue), and —CH₂CH₂OCO—CH═CH₂.

The monomer having a crosslinkable group for the polymeric resin forundercoating preferably is an ester or amide of acrylic or methacrylicacid which has any of the crosslinkable groups shown above.

The content of crosslinkable groups in the polymeric resin forundercoating (the content of radical-polymerizable unsaturated bonds asdetermined by iodometric titration) is preferably 0.1-10.0 mmol, morepreferably 1.0-7.0 mmol, most preferably 2.0-5.5 mmol, per g of thepolymeric resin. When the crosslinkable-group content is within thisrange, satisfactory sensitivity and unsusceptibility to scumming arereconciled and satisfactory storage stability is obtained.

The polymeric resin for undercoating has a mass-average molecular weightof preferably 5,000 or higher, more preferably 10,000-300,000, and anumber-average molecular weight of preferably 1,000 or higher, morepreferably 2,000-250,000. The polydispersity coefficient (mass-averagemolecular weight/number-average molecular weight) thereof is preferablyfrom 1.1 to 10.

The polymeric resin for undercoating may be any of a random polymer,block polymer, graft polymer, and the like. However, it preferably is arandom polymer.

A known resin having hydrophilic groups may be used as the polymericresin for undercoating in the invention. Examples of such resins includegum arabic, casein, gelatin, starch derivatives, carboxymethyl celluloseand the sodium salt thereof, cellulose acetate, sodium alginate, vinylacetate/maleic acid copolymers, styrene/maleic acid copolymers,poly(acrylic acid)s and salts thereof, poly(methacrylic acid)s and saltsthereof, homopolymer and copolymers of hydroxyethyl methacrylate,homopolymer and copolymers of hydroxyethyl acrylate, homopolymer andcopolymers of hydroxypropyl methacrylate, homopolymer and copolymers ofhydroxypropyl acrylate, homopolymer and copolymers of hydroxybutylmethacrylate, homopolymer and copolymers of hydroxybutyl acrylate,polyethylene glycols, hydroxypropylene polymers, poly(vinyl alcohol)s,hydrolyzed poly(vinyl acetate) having a degree of hydrolysis of 60% bymole or higher, preferably 80% by mole or higher, poly(vinyl formal),poly(vinyl butyral), polyvinylpyrrolidone, homopolymer and copolymers ofacrylamide, homopolymer and copolymers of methacrylamide, homopolymerand copolymers of N-methylolacrylamide, alcohol-soluble nylons, andpolyethers of 2,2-bis(4-hydroxyphenyl)propane with epichlorohydrin.

Polymeric resins for undercoating may be used alone or as a mixture oftwo or more thereof.

The amount of the undercoat layer to be formed (on a solid basis) ispreferably 0.1-100 mg/m², more preferably 1-30 mg/m².

[Platemaking from Lithographic Printing Plate Precursor]

The lithographic printing plate precursor of the invention is imagewiseexposed preferably with an infrared laser.

The infrared laser to be used in the invention is not particularlylimited. However, preferred examples thereof include solid lasers andsemiconductor lasers which emit infrared rays having a wavelength of760-1,200 nm. The output of the infrared laser is preferably 100 mW orhigher. For reducing the period of exposure, it is preferred to use amulti-beam laser device.

The exposure period for each pixel is preferably 20 μsec or shorter. Thequantity of irradiation energy is preferably 10-300 mJ/cm².

After the lithographic printing plate precursor of the invention hasundergone imagewise exposure with an infrared laser, it is used, withoutvia any development step, to conduct printing while supplying anoil-based ink and an aqueous ingredient thereto.

Examples of methods for the process include: a method in which thelithographic printing plate precursor is exposed with an infrared laserand then mounted, without via a development step, on a printing machineto conduct printing; and a method in which the lithographic printingplate precursor is mounted on a printing machine, subsequently exposedwith an infrared laser on the printing machine, and then used to conductprinting without via a development step.

When the lithographic printing plate precursor is imagewise exposed withan infrared laser and an aqueous ingredient and an oil-based ink aresupplied to the exposed precursor to conduct printing without via adevelopment step such as, e.g., a wet development step, then theimage-recording layer in its exposed areas, which has been cured by theexposure, forms oil-based-ink-receiving parts having an oleophilicsurface. On the other hand, in the unexposed areas, the uncuredimage-recording layer is dissolved or dispersed in the aqueousingredient and/or oil-based ink supplied and is thus removed therewithto uncover the hydrophilic surface in these areas.

As a result, the aqueous ingredient adheres to the uncovered hydrophilicsurface, while the oil-based ink adheres to the image-recording layer inthe exposed areas to initiate printing. In this operation, the liquid tobe supplied first to the plate surface may be either the aqueousingredient or the oil-based ink. It is, however, preferred to supply theoil-based ink first from the standpoint of preventing the aqueousingredient from being contaminated with those parts of theimage-recording layer which are located in the unexposed areas. As theaqueous ingredient may be used an ordinary fountain solution forlithographic printing. According to the lithographic printing plateprecursor of the invention, effects of the invention such as, e.g.,stable ink receptibility during printing and high printing durabilityare obtained even with ordinary fountain solutions. It is a matter ofcourse that the lithographic printing process of the invention, whichwill be described below, may be applied thereto. As the oil-based inkmay be used an ordinary printing ink for lithographic printing.

The lithographic printing plate precursor is developed on an offsetpress in the manner described above and directly used for printing onmany sheets.

[Lithographic printing process]

One of the lithographic printing process of the invention ischaracterized in that a lithographic printing plate precursor containinga phosphonium salt represented by formula (1) or (2) in theimage-recording layer and/or protective layer is imagewise exposed,subsequently mounted on a printing machine without via a developmentstep, and then used to conduct printing, or that the lithographicprinting plate precursor is mounted on a printing machine, subsequentlyimagewise exposed, and then used to conduct printing.

The other lithographic printing process of the invention ischaracterized in that a fountain solution containing the phosphoniumsalt is used in on-press development. The other steps beginning withimagewise exposure and ending with printing can be conducted in the samemanners as for the platemaking from the lithographic printing plateprecursor. According to this lithographic printing process, effects ofthe invention such as, e.g., stable ink receptibility during printingare obtained even when a lithographic printing plate precursor notcontaining the phosphonium salt is used.

In the fountain solution according to the invention which contains thephosphonium salt, the ingredients given in, e.g., JP-A-5-112085 andJP-A-6-183171 can be suitably used besides the phosphonium salt.

For example, (a) a hydrophilic polymeric compound having film-formingproperties is usable. Preferred examples thereof include cellulosederivatives such as hydroxyethyl cellulose, hydroxypropyl cellulose,methyl cellulose, hydroxypropyl methyl cellulose, hydroxybutyl methylcellulose, and glyoxal modifications of these cellulose derivatives, thedegree of substitution of each cellulose derivative being 20-90%.Especially preferred of these derivatives is hydroxypropyl cellulose.These derivatives may be used alone or in combination of two or morethereof. A preferred range of the amount of the cellulose derivatives tobe used is 0.1-10% by mass.

Water-soluble polymeric compounds other than cellulose derivatives canbe further used. Examples thereof include natural polymers andmodifications thereof, such as gum arabic, starch derivatives (e.g.,dextrin, dextrin obtained by enzymatic decomposition, hydroxypropylateddextrin obtained by enzymatic decomposition, carboxymethylated starch,starch phosphate, and starch octenylsuccinate), alginic acid salts, andcellulose derivatives (e.g., carboxymethyl cellulose, carboxyethylcellulose, and methyl cellulose) and synthetic polymers such aspolyethylene glycol and copolymers thereof, poly(vinyl alcohol) andderivatives thereof, polyvinylpyrrolidone, polyacrylamide and copolymersthereof, poly(acrylic acid) and copolymers thereof, vinyl methylether/maleic anhydride copolymers, vinyl acetate/maleic anhydridecopolymers, and poly(styrenesulfonic acid) and copolymers thereof. Thesepolymeric compounds may be used alone or as a mixture of two or morethereof. The concentration of such polymeric compounds in the fountainsolution composition during use is desirably in the range of 0.005-1% bymass.

(b) A pH buffer is usable. Examples thereof include water-solubleorganic acids and inorganic acids and salts thereof. A pH buffer iseffective in the pH regulation or pH buffering of the fountain solutionand in moderately etching a support for the lithographic printing plateor preventing the support from corroding. Preferred examples of theorganic acids include citric acid, ascorbic acid, malic acid, tartaricacid, lactic acid, acetic acid, gluconic acid, hydroxyacetic acid,oxalic acid, malonic acid, maleic acid, levulinic acid, phytic acid, andorganic phosphonic acids. Examples of the inorganic acids includephosphoric acid, nitric acid, and sulfuric acid. It is also preferred touse alkali metal salts, alkaline earth metal salts, ammonium salts, ororganic amine salts of these organic acids and/or inorganic acids. Theseorganic acids, inorganic acids, ad/or salts thereof may be used alone orin combination of two or more thereof. It is also possible to use alkalimetal hydroxides, phosphoric acid, alkali metal salts, alkali metalcarbonates, silicic acid salts, and the like.

(c) A compound for further improving the wettability of dampeningrollers to realize stable water supply is usable. Examples thereofinclude propylene glycol, dipropylene glycol, tripropylene glycol,tetrapropylene glycol, propylene glycol monomethyl ether, dipropyleneglycol monomethyl ether, tripropylene glycol monomethyl ether,tetrapropylene glycol monomethyl ether, propylene glycol monoethylether, dipropylene glycol monoethyl ether, tripropylene glycol monoethylether, tetrapropylene glycol monoethyl ether, propylene glycolmonopropyl ether, dipropylene glycol monopropyl ether, tripropyleneglycol monopropyl ether, tetrapropylene glycol monopropyl ether,propylene glycol monoisopropyl ether, dipropylene glycol monoisopropylether, tripropylene glycol monoisopropyl ether, tetrapropylene glycolmonoisopropyl ether, propylene glycol monobutyl ether, dipropyleneglycol monobutyl ether, tripropylene glycol monobutyl ether,tetrapropylene glycol monobutyl ether, propylene glycol monoisobutylether, dipropylene glycol monoisobutyl ether, tripropylene glycolmonoisobutyl ether, tetrapropylene glycol monoisobutyl ether, propyleneglycol mono-tert-butyl ether, dipropylene glycol mono-tert-butyl ether,tripropylene glycol mono-tert-butyl ether, tetrapropylene glycolmono-tert-butyl ether, and polypropylene glycols having a molecularweight of 200-1,000 and the monomethyl ethers, monoethyl ethers,monopropyl ethers, monoisopropyl ethers, and monobutyl ethers thereof.These compounds may be used alone or in combination of two or morethereof. The amount of such compounds to be used is preferably in therange of 10-70% by mass. Especially preferred of those compounds areones whose 0.1-0.5% by mass aqueous solutions have a surface tension of55 dyne/cm or lower.

(d) A compound useful in fountain solution concentration is usable.Examples thereof include 3-methoxybutanol, 3-ethoxybutanol,3-propoxybutanol, 3-methyl-3-methoxybutanol, 3-methyl-3-ethoxybutanol,and 3-methyl-3-propoxybutanol. These compounds can be advantageouslyused either alone or in combination of two or more thereof. The amountof these compounds to be used is preferably in the range of 0.1-20% bymass.

(e) A compound effective in preventing the image areas of the printingplate from being deteriorated by solvent residues resulting from waterevaporation is usable. Examples thereof include benzenesulfonic acid,p-toluenesulfonic acid, xylenesulfonic acid, cumenesulfonic acid,benzoic acid, salicylic acid, isophthalylsulfonic acid, gallic acid,phenolsulfonic acid, thiosalicylic acid,4-(butylphenyl)-2-hydroxybenzenesulfonic acid,4-(butylphenyl)benzenesulfonic acid, and (diphenyl ether)sulfonic acid.Furthermore, alkali metal salts (Na, K, and Li salts) and ammonium saltsof these acids can be effectively used. The amount of these compounds tobe used is preferably in the range of 0.01-7% by mass. These compoundsmay be used in combination of two or more thereof.

Besides the ingredients described above, a salt effective in preventingthe corrosion of the printing plate and corrosion of metals used in theprinting machine can be used. Examples thereof include sodium nitrate,potassium nitrate, ammonium nitrate, magnesium nitrate, calcium nitrate,beryllium nitrate, aluminum nitrate, zinc nitrate, zirconium nitrate,nickel nitrate, manganese nitrate, and chromium nitrate. These salts maybe used alone or in combination of two or more thereof.

A surfactant may be further added. Examples of usable anionicsurfactants include fatty acid salts, abietic acid salts,hydroxyalkanesulfonic acid salts, alkanesulfonic acid salts,dialkylsulfosuccinic acid salts, (linear alkyl)benzenesulfonic acidsalts, (branched alkyl)benzenesulfonic acid salts,alkylnaphthalenesulfonic acid salts,alkylphenoxypolyoxyethylenepropylsulfonic acid salts, polyoxyethylenealkylsulfophenyl ether salts, N-methyl-N-oleyltaurine sodium salts,N-alkylsulfosuccinic acid monoamide disodium salt, petroleumsulfonicacid salts, sulfonated castor oil, sulfonated tallow oil, sulfuric acidester salts of fatty acid alkyl esters, alkylsulfuric acid ester salts,polyoxyethylene alkyl ether sulfuric acid ester salts, fatty acidmonoglyceride sulfuric acid ester salts, polyoxyethylene alkylphenylether sulfuric acid ester salts, polyoxyethylene styrylphenyl ethersulfuric acid ester salts, alkylphosphoric acid ester salts,polyoxyethylene alkyl ether phosphoric acid ester salts, polyoxyethylenealkylphenyl ether phosphoric acid ester salts, partly saponifiedstyrene/maleic anhydride copolymers, partly saponified olefin/maleicanhydride copolymers, and naphthalenesulfonic acid salt/formalincondensates. Especially preferred of these are dialkylsulfosuccinic acidsalts, alkylsulfuric acid ester salts, and alkylnaphthalenesulfonic acidsalts.

Examples of usable nonionic surfactants include polyoxyethylene alkylethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene-polystyrylphenyl ethers, polyoxyethylene-polyoxypropylene alkyl ethers, partialfatty acid esters of glycerol, partial fatty acid esters of sorbitan,partial fatty acid esters of pentaerythritol, fatty acid monoesters ofpropylene glycol, partial fatty acid esters of sucrose, partial fattyacid esters of polyoxyethylene-sorbitan, partial fatty acid esters ofpolyoxyethylene-sorbitol, fatty acid esters of polyethylene glycol,partial fatty acid esters of polyglycerol, polyoxyethylated castor oils,partial fatty acid esters polyoxyethylene-glycerol, fatty aciddiethanolamides, N,N-bis-2-hydroxyalkylamines, polyoxyethylenealkylamines, fatty acid esters of triethanolamaine, and trialkylamineoxides. Fluorochemical surfactants and silicone surfactants are alsousable. Preferred of these are polyoxyethylene alkylphenyl ethers,polyoxyethylene/polyoxypropylene block polymers, and the like.

Examples of usable cationic surfactants include alkylamine salts,quaternary ammonium salts, polyoxyethylene alkylamine salts, andpolyethylene polyamine derivatives. The content of such surfactants isdesirably 10% by mass or lower, preferably 0.01-3.0% by mass, from thestandpoint of foaming.

It is preferred to use ethylene glycol, triethylene glycol, butyleneglycol, hexylene glycol, octanediol, diethylene glycol, glycerol,trimethylolpropane, diglycerol, or the like as a wetting agent. Thesewetting agents may be used alone or in combination of two or morethereof. It is generally preferred to use the wetting agent in an amountof 0.1-25% by mass.

Furthermore, a chelate compound may be added to the fountain solutioncomposition according to the invention. The fountain solutioncomposition is usually used after having been diluted with tap water,well water, or the like. The calcium ions and other impurities containedin the tap water or well water used for the dilution may adverselyinfluence printing and be causative of fouled printed matters. In suchcases, this trouble can be eliminated by adding a chelate compound.Preferred examples of the chelate compound includeethylenediaminetetraacetic acid and the potassium salt and sodium saltthereof; diethylenetriaminepentaacetic acid and the potassium salt andsodium salt thereof; triethylenetetraminehexaacetic acid and thepotassium salt and sodium salt thereof;hydroxyethylethylenediaminetriacetic acid and the potassium salt andsodium salt thereof; nitrilotriacetic acid and the sodium salt thereof;organic phosphonic acid compounds such as1-hydroxyethane-1,1-diphosphonic acid and the potassium salt and sodiumsalt thereof and aminotri(methylenephosphonic acid) and the potassiumsalt and sodium salt thereof; and phosphonoalkanetricarboxylic acids.Also effective are organic amine salts, in place of sodium salts orpotassium salts, of these chelating agents. A chelating agent which isstably present in the fountain solution composition and does notadversely influence printing is selected from those chelating agents.

A rust preventive may be used in the fountain solution compositionaccording to the invention. Examples thereof include benzotriazole,5-methylbenzotriazole, 5-methoxybenzotriazole, 4-chlorobenzotriazole,4-bromobenzotriazole, 4-bromo-6-methylbenzotriazole, and4-bromo-6-trifluoromethylbenzotriazole. Examples thereof further includethe compounds formed by replacing the 1-position hydrogen atom of thosecompounds by an alkali metal (K, Na, or Li) or NH₄, benzimidazole andderivatives thereof, mercapto compounds and/or thioether compounds suchas mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionicacid, 4-mercaptobutanoic acid, 2,4-dimercaptobutanoic acid,2-mercaptotetradecanoic acid, 2-mercaptomyristic acid, mercaptosuccinicacid, 2,3-dimercaptosuccinic acid, cysteine, N-acetylcysteine,N-(2-mercaptopropionyl)glycine, N-(2-mercapto-2-methylpropionyl)glycine,N-(3-mercaptopropionyl)glycine,N-(2-mercapto-2-methylpropionyl)cysteine, penicillamine,N-acetylpenicillamine, glycine/cysteine/glutamine condensates,N-(2,3-dimercaptopropionyl)glycine, 2-mercaptonicotinic acid,thiosalicylic acid, 3-mercaptobenzoic acid, 4-mercaptobenzoic acid,3-carboxy-2-mercaptopyridine, 2-mercaptobenzothiazole-5-carboxylic acid,2-mercapto-3-phenylpropanoic acid, 2-mercapto-5-carboxyethylimidazole,5-mercapto-1-(4-carboxyphenyl)tetrazole,N-(3,5-dicarboxyphenyl)-2-mercaptotetrazole,2-(1,2-dicarobxyethylthio)-5-mercapto-1,3,5-thiadiazole,2-(5-mercapto-1,3,4-thiadiazolylthio)hexanoic acid,2-mercaptoethanesulfonic acid, 2,3-dimercapto-1-propanesulfonic acid,2-mercaptobeneznesulfonic acid, 4-mercaptobenzenesulfonic acid,3-mercapto-4-(2-sulfophenyl)-1,2,4-triazole,2-mercaptobenzothiazole-5-sulfonic acid,2-mercaptobenzimidazole-6-sulfonic acid, mercaptosuccinimide,4-mercaptobenzenesulfonamide, 2-mercaptobenzimidazole-5-sulfonamide,3-mercapto-4-(2-(methylaminosulfonyl)ethoxy)toluene,3-mercapto-4-(2-(methylsulfonylamino)ethoxy)toluene,4-mercapto-N-(p-methylphenylsulfonyl)benzamide, 4-mercaptophenol,3-mercaptophenol, 2-mercaptophenol, 3,4-dimercarptotoluene,2-mercaptohydroquinone, 2-thiouracil, 3-hydroxy-2-mercaptopyridine,4-hydroxythiophenol, 4-hydroxy-2-mercaptopyrimidine,4,6-dihydroxy-2-mercaptopyrimidine, 2,3-dihydroxypropyl mercaptan,2-mercapto-4-octylphenyl methane sulfonylaminoethyl ether,2-mercapto-4-octylphenol methaneaminosulfonylbutyl ether, thiodiglycolicacid, thiodiphenol, 6,8-dithiooctanoic acid,5-methoxy-2-mercaptobenzimidazole, 2-mercaptobenzimidazole-5-sulfonicacid, and alkali metal salts, alkaline earth metal salts, ammoniumsalts, and organic amine salts of these compounds. The content of thosecompounds is preferably in the range of 0.0001-5% by mass. Thosecompounds may be used alone or as a mixture of two or more thereof.

Various colorants, antifoamers, and antiseptics and the like can befurther added to the fountain solution composition according to theinvention. For example, dyes for foods can be advantageously used as thecolorants. Examples thereof include yellow dyes such as C.I. Nos. 19140and 15985, red dyes such as C.I. Nos. 16185, 45430, 16255, 45380, and45100, violet dyes such as C.I. No. 42640, blue dyes such as C.I. Nos.42090 and 73015, and green dyes such as C.I. No. 42095. Preferredantifoamers are silicone antifoamers. The silicone antifoamers are ofthe emulsion/dispersion type, solution type, etc., and any of these isusable.

An optimal range of the addition amount thereof is from 0.001-1% bymass.

Examples of the antiseptics include phenol and derivatives thereof,formalin, imidazole derivatives, sodium dehydroacetate,4-isothiazolin-3-one derivatives, benzotriazole derivatives, derivativesof amidine or guanidine, quaternary ammonium salts, derivatives ofpyridine, quinoline, or guanidine, derivatives of diazines or triazoles,and derivatives of oxazole or oxazine.

The ingredients described above are dissolved in water, preferably indesalted water, i.e., pure water, to give an aqueous solution. Thus, thefountain solution composition for use in the invention is obtained. Whena concentrate is used, it is preferred from the standpoint ofprofitability that the concentrate be diluted 10-100 times with tapwater, well water, or the like before use.

EXAMPLES

The invention will be explained below by reference to Examples, but theinvention should not be construed as being limited to the followingExamples.

1. Production of Support

An aluminum sheet (material, 1050) having a thickness of 0.3 mm wassubjected to a degreasing treatment with 10% by mass aqueous sodiumaluminate solution at 50° C. for 30 seconds in order to remove therolling oil remaining on the surface thereof. Thereafter, the aluminumsurface was grained with three brushes having nylon bundles set thereinhaving a bristle diameter of 0.3 mm and with an aqueous suspension ofpumice having a median diameter of 25 μm (specific gravity of thesuspension, 1.1 g/cm³), and then sufficiently washed with water. Thissheet was immersed for 9 seconds in 25% by mass aqueous sodium hydroxidesolution having a temperature of 45° C. to conduct etching and thenwashed with water. Thereafter, the sheet was immersed in 20% by massnitric acid at 60° C. for 20 seconds and washed with water. In thisoperation, the amount of the grained surface layer removed by etchingwas about 3 g/m².

Subsequently, an electrochemical surface-roughening treatment wascontinuously conducted using a 60-Hz AC voltage. The electrolyticsolution used for this treatment was 1% by mass aqueous nitric acidsolution (containing 0.5% by mass aluminum ions) and the temperature ofthe solution was 50° C. The AC power source used was one providing atrapezoidal rectangular wave alternating current wherein the TP, whichis the time required for the current value to increase from zero to apeak, was 0.8 msec and the duty ratio was 1:1.

A carbon electrode was used as a counter electrode to conduct theelectrochemical surface-roughening treatment using ferrite as anauxiliary anode. The current density was 30 A/dm² in terms of peakvalue. To the auxiliary anode was supplied 5% of the current flowingfrom the power source. The quantity of electricity in the nitric acidelectrolysis was 175 C/dm² in terms of the quantity of electricity atthe time when the aluminum sheet was functioning as an anode. After thistreatment, the aluminum sheet was washed with water by spraying.

Thereafter, an electrochemical surface-roughening treatment with anelectrolytic solution consisting of 0.5% by mass aqueous hydrochloricacid solution (containing 0.5% by mass aluminum ions) and having atemperature of 50° C. was conducted under the conditions of a quantityof electricity of 50 C/dm² at the time when the aluminum sheet wasfunctioning as an anode, in the same manner as in the nitric acidelectrolysis. The sheet was then water-washed by spraying. This sheetwas subjected to direct-current anodization at a current density of 15A/dm² using 15% by mass sulfuric acid (containing 0.5% by mass aluminumions) as an electrolytic solution to deposit an anodized coating in anamount of 2.5 g/m², subsequently washed with water, and dried. Theresultant support is referred to as support A. This substrate wasexamined for center-line average surface roughness (Ra) with a pointerhaving a diameter of 2 μm. As a result, the average surface roughnessthereof was found to be 0.51 μm.

The following undercoating fluid (1) was applied to the support in anamount of 6 mg/m² on a dry basis to form an undercoat layer comprising awater-soluble polymer. Thus, undercoated supports for use in thefollowing experiments were produced.

Undercoating Fluid (1) Undercoating compound (1) 0.017 g Methanol  9.00g Water  1.00 g

Undercoating compound (1)

2. Production of Lithographic Printing Plate Precursors Examples 1 to 6

An image-recording-layer coating fluid (1) which had the followingcomposition was applied by bar coating on the support having anundercoat layer and then dried in an oven at 100° C. for 60 seconds toform an image-recording layer in an amount of 1.0 g/m² on a dry basis.The image-recording-layer coating fluid (1) was obtained, just beforeapplication, by mixing the following photosensitive liquid (1) with thefollowing microcapsule suspension (1) and stirring the mixture.

Photosensitive Liquid (1) Binder polymer (1) 0.162 g Polymerizationinitiator (1) 0.160 g Polymerization initiator (2) 0.180 g Infraredabsorber (1) 0.020 g Polymerizable compound Aronix M-215 0.385 g(manufactured by Toagosei Co., Ltd.) Fluorochemical surfactant (1) 0.044g Methyl ethyl ketone 1.091 g 1-Methoxy-2-propanol 8.210 g Phosphoniumsalt shown in Table 1 Amount shown in Table 1 Microcapsule Suspension(1) Microcapsules (1) synthesized in the manner 2.640 g shown belowWater 2.425 g

Binder polymer (1)

Polymerization initiator (1)

Polymerization initiator (2)

Infrared absorber (1)

Fluorochemical surfactant (1)

Synthesis of Microcapsules (1)

In 16.67 g of ethyl acetate were dissolved 10 g of atrimethylolpropane/xylene diisocyanate adduct (Takenate D-110N,manufactured by Mitsui Takeda Chemicals, Inc.; 75% by mass ethyl acetatesolution), 6.00 g of Aronix SR-399 (manufactured by Toagosei Co., Ltd.),and 0.12 g of Pionin A-41C (manufactured by Takemoto Oil & Fat Co.,Ltd.). Thus, an oily-phase ingredient was prepared. On the other hand, a4% by mass aqueous solution of PVA-205 was prepared as an aqueous-phaseingredient in an amount of 37.5 g. The oily-phase ingredient was mixedwith the aqueous-phase ingredient, and this mixture was emulsified bytreatment with a homogenizer at 12,000 rpm for 10 minutes. The emulsionobtained was added to 25 g of distilled water, and this mixture wasstirred at room temperature for 30 minutes and then at 40° C. for 2hours. The microcapsule suspension thus obtained was diluted withdistilled water so as to result in a solid concentration of 15% by mass.The average particle diameter of the microcapsules was 0.2 μm.

The protective-layer coating fluid (1) shown below was applied on theimage-recording layer by bar coating and then dried in an oven at 125°C. for 75 seconds to form a protective layer in an amount of 0.15 g/m²on a dry basis. Thus, a lithographic printing plate precursor wasobtained.

Protective-Layer Coating Fluid (1) Poly(vinyl alcohol) (PVA 105, 2.24 gmanufactured by Kuraray Co., Ltd.; degree of saponification, 98.5 mol %;degree of polymerization, 500) 6% by mass aqueous solutionPolyvinylpyrrolidone (K30) 0.0053 g Surfactant (Emalex 710, 2.15 gmanufactured by Kao Corp.) 1% by mass aqueous solution Flaky syntheticmica (MEB 3L, 3.75 g manufactured by UNICOO Co., Ltd.; average particlediameter, 1-5 μmφ) 3.4% by mass aqueous dispersion Distilled water 10.60g

Examples 7 to 12

An image-recording-layer coating fluid (2) which had the followingcomposition was applied by bar coating on the support having anundercoat layer and then dried in an oven at 100° C. for 60 seconds toform an image-recording layer in an amount of 1.3 g/m² on a dry basis.Furthermore, a protective layer was formed in the same manner as inExample 1 to obtain a lithographic printing plate precursor.

The image-recording-layer coating fluid (2) was obtained, just beforeapplication, by mixing the following photosensitive liquid (2) with themicrocapsule suspension (1) and stirring the mixture.

Photosensitive Liquid (2) Binder polymer (1) 0.162 g Polymerizationinitiator (3) 0.180 g Infrared absorber (2) 0.038 g Polymerizablecompound Aronix M-215 0.385 g (manufactured by Toagosei Co., Ltd.)Fluorochemical surfactant (1) 0.044 g Methyl ethyl ketone 1.091 g1-Methoxy-2-propanol 8.210 g Phosphonium salt shown in Table 1 Amountshown in Table 1

Polymerization initiator (3)

Infrared absorber (2)

Comparative Example 1

A lithographic printing plate precursor for comparison was obtained inthe same manner as in Example 1, except that the phosphonium salt in thephotosensitive liquid (1) was omitted.

Comparative Example 2

A lithographic printing plate precursor for comparison was obtained inthe same manner as in Example 7, except that the phosphonium salt in thephotosensitive liquid (2) was omitted.

Example 13

The protective-layer coating fluid (2) shown below was applied on thesame image-recording layer as in Comparative Example 2 by bar coatingand then dried in an oven at 125° C. for 75 seconds to form a protectivelayer in an amount of 0.15 g/m² on a dry basis. Thus, a lithographicprinting plate precursor was obtained.

Protective-Layer Coating Fluid (2) Poly(vinyl alcohol) (PVA 105, 2.24 gmanufactured by Kuraray Co., Ltd.; degree of saponification, 98.5 mol %;degree of polymerization, 500) 6% by mass aqueous solutionPolyvinylpyrrolidone (K30) 0.0053 g Surfactant (Emalex 710, 2.15 gmanufactured by Kao Corp.) 1% by mass aqueous solution Flaky syntheticmica (MEB 3L, 3.75 g manufactured by UNICOO Co., Ltd.; average particlediameter, 1-5 μmφ) 3.4% by mass aqueous dispersion Phosphonium compound(P-8) 0.20 g Distilled water 10.60 g

3. Evaluation of Lithographic Printing Plate Precursors

The lithographic printing plate precursors obtained above were examinedand evaluated for on-press developability and printing durability by thefollowing methods. The results obtained are shown in Table 1.

<On-Press Developability>

Each of the lithographic printing plate precursors obtained was exposedwith Trendsetter 3244VX, manufactured by Creo Co., Ltd. and equippedwith a 40-W infrared semiconductor laser of the water cooling type. Theexposure was conducted under the conditions of an output of 9.6 W,outer-drum rotational speed of 150 rpm, and resolution of 2,400 dpi. Theexposed plate precursor was attached to the cylinder of printing machineSOR-M, manufactured by Heidelberg. A fountain solution [Ecolity 2(etchant manufactured by Fuji Photo Film Co., Ltd.)/water=2/98 (volumeratio)] and black ink TRANS-G(N) (manufactured by Dainippon Ink &Chemicals, Inc.) were supplied thereto. Thereafter, printing wasconducted on 100 sheets at a printing speed of 6,000 sheets per hour.The number of sheets of printing paper required before the unexposedareas of the image-recording layer were completely removed bydevelopment on the printing machine and came not to transfer the ink tothe printing paper was counted as a measure of on-press developability.

<Printing Durability>

After the evaluation of on-press developability, printing was furthercontinued. As the number of printed sheets increased, the ink density inthe printing paper decreased. Printing durability was evaluated in termsof the number of printed sheets required for the ink density (reflectiondensity) to decrease by 0.1 from the density as measured at printinginitiation.

TABLE 1 Amount of On-press addition develop- Printing Phos- to photo-ability durability phonium sensitive (number of (number of salt liquid(g) sheets) sheets) Example 1 P-1 0.032 30 5500 Example 2 P-3 0.04 286000 Example 3 P-7 0.062 19 6500 Example 4 P-8 0.05 15 7000 Example 5P-9 0.068 17 6800 Example 6 P-11 0.072 20 6300 Comparative no addition30 3000 Example 1 Example 7 P-1 0.032 32 6000 Example 8 P-4 0.041 306200 Example 9 P-6 0.042 25 6000 Example 10 P-5 0.048 30 5800 Example 11P-14 0.038 20 6200 Example 12 P-8 0.05 16 6800 Comparative no addition32 1000 Example 2 Example 13 P-8 0.20(*1) 19 6500 (*1)addition toprotective-layer coating fluidThe following can be seen from Table 1. As compared with thelithographic printing plate precursors heretofore in use (ComparativeExamples 1 and 2), the lithographic printing plate precursors of theinvention attain highly excellent printing durability (inkreceptibility) while retaining on-press developability. Furthermore, asapparent from Examples 1 to 6 and Examples 7 to 12, the lithographicprinting plate precursors employing the phosphonium salts represented byformula (2) show better on-press developability than the lithographicprinting plate precursors employing the other phosphonium salts.

Example 14 and Comparative Example 3

In Example 14, the same procedure as in Comparative Example 2 wasconducted, except that the fountain solution was replaced by oneobtained by diluting liquid a shown in the following Table 2 with waterto 3% by volume. In Comparative Example 3, the same procedure as inComparative Example 2 was conducted, except that the fountain solutionwas replaced by one obtained by diluting liquid β shown in the followingTable 2 with water to 3% by volume. The results obtained are shown inTable 3.

TABLE 2 Liquid α Liquid β Pure water 35.6 36.6 Propylene glycolmono-n-butyl ether 28.4 28.4 Propylene glycol 25 25 Octane diol 4.7 4.7Glycerol 1 1 Maleic acid 1.9 1.9 KOH (48% by mass aqueous solution) 2.32.3 Ammonium nitrate 0.3 0.3 Ammonium secondary phosphate 0.3 0.3Magnesium sulfate 0.8 0.8 Citric acid 0.2 0.2 Ammonium secondary citrate0.7 0.7 Phosphonium salt (P-8) 0.1 0 1,2-Benzisothiazol-3(2H)-one 0.60.6 Total 100 100

TABLE 3 Kind of On-press fountain developability Printing durabilitysolution (number of sheets) (number of sheets) Example 14 liquid α 327000 Comparative liquid β 32 1000 Example 3

It can be seen from Table 3 that the on-press development typelithographic printing process of the invention employing a fountainsolution containing a phosphonium salt attains highly excellent printingdurability (ink receptivity) while maintaining on-press developabilityas compared with the process employing an ordinary fountain solution(Comparative Example 3).

According to the invention, a lithographic printing plate precursor canbe provided which gives a lithographic printing plate stably showing inkreceptibility during printing and having excellent printing durability.The invention can further provide a lithographic printing plateprecursor in which an image can be recorded with a laser and which,after the image recording, can be satisfactorily developed on a printingmachine without via a development step to give a printing plate stablyshowing ink receptibility during printing and having excellent printingdurability. The invention can furthermore provide a lithographicprinting process which includes image recording with a laser andon-press development and which attains excellent printing durabilitywhile maintaining satisfactory on-press developability.

The entire disclosure of each and every foreign patent application fromwhich the benefit of foreign priority has been claimed in the presentapplication is incorporated herein by reference, as if fully set forth.

What is claimed is:
 1. A phosphonium salt represented by formula (2):

wherein Ar₁ to Ar₆ each independently represents a phenyl group; Lrepresents —(CH₂)₉—; R represents an alkyl group, an aryl group, aheterocyclic group, an alkoxy group, an alkylamino group or an arylaminogroup; n represents an integer of from 1 to 3; and m is a numbersatisfying n×m=2.
 2. The phosphonium salt according to claim 1, whereina sulfonate anion in the formula (2) is represented by one selected fromthe following structural formulae:


3. The phosphonium salt according to claim 1, wherein a sulfonate anionin the formula (2) is represented by one selected from the followingstructural formulae: